Character Limit
Increase the character limit from 18 to at least 36, I would prefer 40 so I can have 4 of every race, two males and two females, but I can settle for 36 to have 6 of every class. Each class would have a dedicated tank build, a hybrid Stamina/Magicka build, one Stamina build with two-handed, one Stamina build with dual-wield, one Magicka build focused on healing/class skills, and one Magicka build focused on damage. I know I could always use a second account, but they don't share champion points, companions, or any collectibles; I would like everything available that I have already built up on a single account instead of trying to split it.
Companions
More companions, at least one for every class, maybe a vampire or werewolf too but not necessary. I would also like to have more than one at a time following me, up to 3 active at once while playing solo so I can feel like my own party without actually teaming up with other players. I play at odd hours of the day so finding another player isn't always an option and my lack of focus makes me jump from one character to another frequently, that can be annoying with another real person having to deal with my constant changing of characters. At least I know my party of companions would always be there willing to join whoever I decide to play.
Multi-Floor Dungeon
First game to experience something like this was back in 1996 on the SNES with Lufia 2's Ancient Cave. It's one of those multiple level dungeons where mobs get increasingly harder the deeper you go down, I like to see something like this added to ESO. Following the same rules as Public Dungeons so they aren't private instances, you can encounter other players or groups inside of it outside of your own. At least have 5 floors, would prefer as many as 10 floors with ever increasing difficulty of larger trash packs and more powerful bosses the further you explore.