Diablo III: Reaper of Souls

At this point, we're currently planning that unidentified legacy Legendaries will also not provide new item appearances for Transmogrification. Our reasoning is this: even old Legendaries will be following new rules once we release Loot 2.0 and we want Transmogrification to reflect what new items you've gotten after that point.

http://us.battle.net/d3/en/forum/topic/1...269?page=4

So there's no reason to collect unids unless they change this again. They've also removed BoA on transmog.