With Blizzard trying to make every spec viable for PvE and PvP (not successfully, but it seems better than ever) it seems like a perfectly reasonable thing to do.
With warlocks in particular, all 3 specs have their niche. This prompts us to switch spec from fight to fight based on the mechanics. Or perhaps 2 PvE specs and a PvP one on the side.
Whatever the case, it seems now more than ever it should be implemented.