I like the possibilities that modifiable UI implementations open up (though I am against it, more later). In the long-run it can greatly better the game in general by not only providing good ideas to the developers of the game, but also testing them.

But the reason why I'm against implementation is that this also opens up the possibility of "boss mods", which can make encounters significantly easier depending on what SE's framework allows (i.e. tracking ability cooldowns, UI "announcements", etc). Granted, this can be dealt with by making encounters very hard and intensive (which is good IMO), but somewhat impossible to defeat without the mods (or a professional group of players to work with )