I think it would be best if they did it in a DLC so we can choose if we want it or not. Say maybe every 6 months or once a year, a new Perk Tree comes out so our playing style will be different and "refresh" the game like what Blizzard did with Diablo II or how they improved Civ V with their Civs (or what ever they called it) Tree.
I think it would be a great idea, but only as a DLC so this way we can turn it on/off just in case we don't like it and prefer the older ones.
So what do you guys and gals think?