Let me started by saying that I've played ESO on and off since beta. I pay for ESO plus and have probably 60-70% of the time since early 2014.
There are some quality of life changes that have been made recently that are great. A recent small change that was great is when improving items when crafting, Summerset made it so that this is already at the required amount of tempers for 100%. You now don't have to click 8-10 times to get to 100%.
Here are a few changes I'd personally like to see added to the game staying away from balance and stuff. I've seen all/most of these suggested before at some point.
Enable players to hide vampire appearance
There are skins already in game that hide this, so why not? I'd like more options on how my character can look. We can now disguise axes as swords etc.. Can't really see this being any different.
I would pay crowns for this.Make mount speed etc account wide
The WORST thing about levelling a new character. I don't mind undaunted, psyjic order etc but having to upgrade my mount separately is a bigger grind than anything in the game. As the game ages, people get less tolerant of a grinding like this for every character or alt.
Mementos don't last long enough/aren't valuable enough
Wild Hunt Aura and Storm Atro etc should last around the same time as food, if for no other reason to make them more valuable. Personally, if a memento drops in a crate or something it's a little... Meh. I'd rather have some riding lessons (see above).
Make more outfits slots hideable
Again, just more character customisation options. Let us hide chest for a musclebound nord warrior for example.
Alliance change token
Race change is already a thing. This wouldn't even change any passives. I started in 2014 with an all AD guild. Now a lot of my guild player on a different alliance to my main.
I would pay crowns for this.Make dungeon gear BoE
Trials gear I understand but think about making dungeon gear tradable or craftable (even just weapons/jewelery). I'm currently trying to farm for a Bone Pirate Bow and have ran over 45 runs in the last few weeks. A lot of players have limited time with the game due to work etc and I'd happily pay a lot of gold to another player for this or craft it myself without having to spend all my playtime farming it.
These are just my two cents

Please don't flame me.
///// AD Master Race Since 2014 /////
Sindri al'Atreyu | Wood Elf Templar
Eivii | Wood Elf Nightblade
Saurmia | High Elf Magicka Templar
PC/EU - Beta Tester