if they added it as an alternative alongside the normal dungeons then it wouldnt be a problem much, it would be "optional content".
of course there would be those who would complain about how its bad or not fair X gear is gated by it or how the rng sucks or how they dont want to have to do it to farm tomes fastest etc.
but if anyone inc SE would ever stop to worry about that we would see no new content ideas ever; which would lead to other complaining.
Vicious circle, cant win.

one day they may look into this seriously, although i doubt it will be until post 4.0 due to "ps3 limitations" BS

tbh my ultimate dream would be a Bloody Tower style optional thing, random floors with unknow enemies that could be from anywhere else in the game, and you just see how far you can survive rather than try to actually clear it. i guess it would have to have some basic prize function based upon floors cleared to interest the masses but man id love it just for some leaderboard bragging rights