Good Morning!
I would like to put forth a couple of suggestions as someone who plays ESO primarily as a place for text-based RP. I could be wrong but I feel like ESO has one of the strongest role-playing communities I have seen in an MMO. Despite the amount of RPers there are some small quality of life things that ESO doesn't have, a couple of which can be found in pretty much every other MMO on the market.
The first is dice rolling in the chats.
This isn't even just something that RPers alone would use. Being able to type in a code like /roll 1d20 into the chat and having it roll can be used for more than RP scenarios, but also can be used for any scenario where someone wants a random result. I've never played an MMO that didn't have a built in dice roller, and the one addon dice roller available isn't anything to write home about. I feel like a dice roller in the chat would be a simple thing to add that would be of great value, especially to the RP community.
Next is being able to sit on furniture
This one would not be as easy to implement, but with the advent of player housing on the horizon, I really think it's something that should be looked at. We are going to want to craft beds, chairs, benches, tables and such for our homes, but it would be infinitely better if we could actually use these things. /sitchair is great, but it's awkward trying to sit around a table in a tavern or guild base that is already surrounded by useless chairs that can't be used. Making chairs and benches intractable would be awesome. I know there is the Sit on Benches addon, but it's not the best. Your character sits on the very edge of the seat and looks very weird in most situations.
Torches, Lanterns and other Off-Hand items
Torches, Lanterns, Flowers, Books, and other off-hand items would be wonderful. They could have absolutely no stats and just be aesthetic items you can equip in place of your weapons, or they could be off-hand stat-sticks like in games like World of Warcraft. But being able to walk while carrying a torch or lantern would be fantastic! It would also create a bit of an economy boost because rare items could sell for a decent price in the guild stores. I'd even be fine with them being costume pieces in the crown store if they were entirely cosmetic.
Werewolf Shifting
This one may not be viable the way werewolves work mechanically in the game, but as an avid werewolf RPer I would love to be able to be in werewolf as much as I want/need for RP, Now I of course understand that this probably isn't viable for actual game mechanics, but is there any reason why it wouldn't work to allow the werewolf timer to not start until you enter combat? Here is how I suggest it could work: You hit your ultimate and shift, but your bar doesn't go down until you actually enter combat with another player or mob. Then the timer starts. It doesn't stop, even if you leave combat, it will still run down. And once you've entered combat it functions exactly as it does now. This would allow people to enter werewolf in non-combat situations (like for RP, or taking screen shots, etc) but wont break it mechanically. It'll still cost ultimate, so if you use it out of combat to RP, when you press it again to de-shift back to normal you're still out the ultimate.
Alternatively... you could just make werewolf polymorphs in the crown store. I don't really like suggesting more content for the crown store, but as long as it remains aesthetic. You could have multiple skins, the white, the black, the brown, etc.
Longer guild MotD and member Notes
This isn't exclusively RP-related, but I am constantly running out of MotD and Member Note room. I suppose it's hard to quantify how much is too much it terms of length. Will doubling the space of the MotD increase the stress on the servers? I've no idea. But I'd love some increased length there, and in member notes. It might also help save space if things like the codes to change colors could be removed and replaced with a simple text-editor that allows you to change the colors, sizes and alignments of fonts in the MotD for guilds. I would also personally love to see some kind of player profile UI feature. I certainly wouldn't mind getting an addon, but there just isn't an addon I've found that is like TotalRP or MyRolePlay that have been created for WoW here for ESO.
Guild Search
Another one that isn't exclusively RP-related would be a guild search feature. Allow guilds to write small descriptions of their guild and put it up to help recruit. This could actually be done in game with maybe the same kind of boars where you get your crafting dailies, in most major cities there could be a board you interact with that opens up with UI element for guilds and allows you to search the burbs guilds have posted, and send a request to join.
I also wanted to take a moment to thank ZOS for the features they've added recently that have been amazing boosts for the RP community:
1. Dying Costumes, and Shields
2. Player housing (soon! Yay!)
3. Personalities
4. Appearance, Race and Name Changes
5. Being able to change hairstyles, clothes, adornments, etc in-game!

6. Tattoos! I hope more come soon!
7. Hats!
8. One Tamriel - I know this wasn't aimed at RPers, but in one sweeping change you opened up the ENTIRE community to RP together and that's AMAZING.
So thanks ZOS. You've made ESO a very RP-friendly MMO and I love it. But please, what about those dice rollers in the chat? Pretty please? Pretty pretty pretty please!?
Lüc - Argonian Necromancer Healer
PC-NA