I rather liked the Nine Divines thingy in Morrowind (Imperial Cult), it had fairly peaceful quests were you just collected donations, healed people and, well, just tried to be helpful to those who hit rock bottom instead of slaying monsters they would never meet anyway. It was a nice change from the usual quests.
I put hundreds of hours into Morrowind, but never ended up doing the Imperial Cult quest-line. However from your description, it sounds like I would've loved it. I will add a similar option to the poll (healers guild, donation guild or something, I'll think of a better name before posting; perhaps just Nine Divines guild.)
And then I also want the return of the guilds from Oblivion, but the quests should be more designed around being good with skills. In Oblivion it's possible to become the Arch-Mage without knowing any magic at all, which is extremely silly. That should not be the case, same with Thieves Guild being heavily designed around sneaking. Without a high sneaking skill, they should be rather hard to pull out well without getting seen and penalised or whatever. And so on with the other guilds.
I agree completely. I don't want them to put a minimum skill/attribute on different ranks like they did in Morrowind, but rather force you to have a minimum skill/attribute to complete the quests (of course, it shouldn' be totally limiting, it is an open world after all).
Infact, I think it should be impossible to become the highest ranked member of a guild, that's for the desk people. The player is just a lowly foot soldier following quest orders anyway, it really doesn't make sense to become the leader, especially when you can't do anything with your "power" like giving new quests or whatever. It wasn't possible to become the guild leader in Daggerfall, and I think that was a good design decision.
That would add to the realism apsect, however I've always enjoyed becoming the head of a guild. Although it would be awesome if some real power, and real responsibility came with your position.