I know for sure I want to use one on for a neck and either shoulders or legs. Currently in SimC the 2 piece t15 is worth roughly 3k dps (also note that the proc for the timeless trinket is not in it) if you sim me. Unfortunately there's no weapon or that would be an obvious choice.
Besides 5 Burden of Eternity to use, I also have Grievous Glad pants.
So basically, neck, (shoulders or legs), chest, belt are the only sub 522 pieces, which seem the logical ones to do. Should I drop the 2 piece and use the Grievous pants / Timeless ones?
It's very unfortunate Blizzard decided to exclude weapons and trinkets. For those of us that did a lot of heroics and never got a weapon it really is a kick in the teeth. Honestly I wouldn't worry about it too much. My guess is losing the 2-piece is going to be very close to even and not worth the trouble.