Pillarboxed dialogue is absolutely unacceptable.
Topic on Talk:Mass Effect Legendary Edition
I doubt it - most cutscenes were built with 16:9 in mind - extending this would show weirdness such as preloaded offscreen models or revealing that planet entry cutscenes are just a ship flying infront of a 2D texture.
In original tirlogy mods made cutscenes in-game and dialogues 21:9 as well.