Most of what I have to say regarding plot/information dissemination and character opportunities has has already been said in this post multiple times, so let me just +1 that and be done about it.
But specifically, I want to reply to this answer, because based on information given by the mod team in the past, ranks were indeed used as a guideline to provide certain benefits or plotting opportunities. I'll paste/paraphrase from my personal plurk about the matter:
I have a post I keep on my journal just for housekeeping like my threads and points and misc game info that I keep track of for my own organization. Part of that is that I saved certain links that gave plotting opportunity information that was hard to find otherwise, such as rank benefits. Early on in the game the modteam actually did list the tangible IC benefits for rank ups. All of these posts are publicly available on the regain page, but players would have to dig for them if they wanted to see them. As has been mentioned already, having to dig to find basic information that should be available upfront is extremely frustrating and a recurring theme in this game.
Here are the posts I saved- I kept an eye on the regain post to save a reference once someone got rank within my character's clan for the first time so I would know what I was working towards, so these are sampled from some of the earliest rank ups, up to the first 3*:
1* Sutoku Rank Up Benefits - This post was actually linked into Matoba's own 1* Rankup reply by the mods, as a reference for the specific benefits this rank is entitled to. 2* Sutoku Rank Up Benefits - This one comes from Matoba's own rankup, which iirc was not the first 2* but I happened to remember to save it just then. This one does not list tangible benefits anymore. 3* Sutoku Rank Up Benefits - This one, again, has no standard "list" of tangible benefits, and is moreso flavortext tailored specifically to the character. It does, however, specify access to a specific IC opportunity/resource for that character that I can say with certainty was not provided in Matoba's rankup.
As you can see, the rankups at first listed specific benefits, which are not specifically plot info, but they are IC access to specific things, which affects what a character can be reasonably assumed able to interact with. These benefits seem to be implicitly extended to all characters with that rank.
From the 2* ranking onward there was a noticeable shift in the modteam giving more flavor text-based regain messages that were tailored to the character or regain. Personally, I really loved these! I thought they were a great way to show a character's contributions were appreciated and the character felt like a part of the world. That said, because nothing had been really established clearly as far as what benefits were attached to ranks at that point, this means that early characters may have gotten one idea of the mechanic, while later players might get another impression. I feel this mechanic badly needed a hard clarification of the exact benefits beforehand, and if something changed in how the modteam felt they would be best handled, the entire game really needed to be notified that there had been a change in how these would be considered/handled.
The additional thing I would caution with this format is that tailor-written messages may lead to some feelings of disappointment that certain players are given either more OOC effort or IC resources than others, in the same way that a common feedback on this post is that plot questions are given a different level of effort and care depending on who is asking them. I would advise that the modteam is really cautious about this. These tailored flavortexts are fun on the surface, but can contribute to the sentiment that some players are favored compared to others, and I have been in other games where tailored flavortext/opportunities became a major painpoint for the playerbase as well.
Finally, I wanted to address specifically the assertion that rank has never been considered for access to specific plots. A while back I asked whether rank would be a requirement in order to have Matoba investigate and engage in business with Sutoku's trade boats in order to pursue a player plot that I had thought of, and was told that I would need a 3* Rank to gain the option to access that plot avenue. This directly contradicts what you are saying here that rank does not give the player access to pursue certain things for their characters.
I understand that the way a modteam decides to handle various game mechanics changes over time, but the fact that none of this was defined well to the game at large in a way that players could easily plan out their ranks, both whether they were worth spending the points and what opportunities rank would make available to them, and that there appears to have been either a shift in how the modteam decided to approach ranks or handled that access on a player by player basis, does not paint a pretty picture for players who are putting in the work to pursue those avenues only to feel that it was a waste of their effort and time.
re: rank opportunities
But specifically, I want to reply to this answer, because based on information given by the mod team in the past, ranks were indeed used as a guideline to provide certain benefits or plotting opportunities. I'll paste/paraphrase from my personal plurk about the matter:
I have a post I keep on my journal just for housekeeping like my threads and points and misc game info that I keep track of for my own organization. Part of that is that I saved certain links that gave plotting opportunity information that was hard to find otherwise, such as rank benefits. Early on in the game the modteam actually did list the tangible IC benefits for rank ups. All of these posts are publicly available on the regain page, but players would have to dig for them if they wanted to see them. As has been mentioned already, having to dig to find basic information that should be available upfront is extremely frustrating and a recurring theme in this game.
Here are the posts I saved- I kept an eye on the regain post to save a reference once someone got rank within my character's clan for the first time so I would know what I was working towards, so these are sampled from some of the earliest rank ups, up to the first 3*:
1* Sutoku Rank Up Benefits - This post was actually linked into Matoba's own 1* Rankup reply by the mods, as a reference for the specific benefits this rank is entitled to.
2* Sutoku Rank Up Benefits - This one comes from Matoba's own rankup, which iirc was not the first 2* but I happened to remember to save it just then. This one does not list tangible benefits anymore.
3* Sutoku Rank Up Benefits - This one, again, has no standard "list" of tangible benefits, and is moreso flavortext tailored specifically to the character. It does, however, specify access to a specific IC opportunity/resource for that character that I can say with certainty was not provided in Matoba's rankup.
As you can see, the rankups at first listed specific benefits, which are not specifically plot info, but they are IC access to specific things, which affects what a character can be reasonably assumed able to interact with. These benefits seem to be implicitly extended to all characters with that rank.
From the 2* ranking onward there was a noticeable shift in the modteam giving more flavor text-based regain messages that were tailored to the character or regain. Personally, I really loved these! I thought they were a great way to show a character's contributions were appreciated and the character felt like a part of the world. That said, because nothing had been really established clearly as far as what benefits were attached to ranks at that point, this means that early characters may have gotten one idea of the mechanic, while later players might get another impression. I feel this mechanic badly needed a hard clarification of the exact benefits beforehand, and if something changed in how the modteam felt they would be best handled, the entire game really needed to be notified that there had been a change in how these would be considered/handled.
The additional thing I would caution with this format is that tailor-written messages may lead to some feelings of disappointment that certain players are given either more OOC effort or IC resources than others, in the same way that a common feedback on this post is that plot questions are given a different level of effort and care depending on who is asking them. I would advise that the modteam is really cautious about this. These tailored flavortexts are fun on the surface, but can contribute to the sentiment that some players are favored compared to others, and I have been in other games where tailored flavortext/opportunities became a major painpoint for the playerbase as well.
Finally, I wanted to address specifically the assertion that rank has never been considered for access to specific plots. A while back I asked whether rank would be a requirement in order to have Matoba investigate and engage in business with Sutoku's trade boats in order to pursue a player plot that I had thought of, and was told that I would need a 3* Rank to gain the option to access that plot avenue. This directly contradicts what you are saying here that rank does not give the player access to pursue certain things for their characters.
I understand that the way a modteam decides to handle various game mechanics changes over time, but the fact that none of this was defined well to the game at large in a way that players could easily plan out their ranks, both whether they were worth spending the points and what opportunities rank would make available to them, and that there appears to have been either a shift in how the modteam decided to approach ranks or handled that access on a player by player basis, does not paint a pretty picture for players who are putting in the work to pursue those avenues only to feel that it was a waste of their effort and time.