Don't expect 8 piece armor sets coming back... this Blizzard poster makes a great point on why 5 piece sets are ideal.

The problem with a big 8 piece armor set is that it may cause someone to ignore an item that would be great for them as they are focused on the specific items that will get their set bonus. With the 5 piece sets, players are able to mix and match pieces to fit their style of play better or even help out for the specific encounter they are at.