This has been a topic of hot debate on the Reddit subforum (over 500 comments) as well as Tamriel Foundry (over 800 posts). Primarily the current API giving mod-makers access to information regarding opposing player actions, buffs, and mana/stamina status in PvP.
There has been a lot of back and forth, with people on both extremes (wanting full access to everything, wanting no addons at all) and people wanting to find a middle ground. I'm curious where people here fall, in regards to what features they find acceptable for addons to be able to adjust from the standard UI. The more complex issue being, of course, that it's not as simple as a "don't like it don't use it" situation, because players who want to compete at the highest levels have always been and will always be compelled to use addons of sufficient power in their ability to make the game easier, whether they want to or not, so the simple act of making a feature available to be modded for, in a way can pigeonhole players into using it if powerful enough. Also, if there was an option to create separate PvP campaigns where UI functions were restricted, would that interest you, and if so which would you go with?