For me, big thing is Cyro specific skills and presumably balancing. I've done most PvE content, aside from the last few HMs and perfectas, and I always end up back in Cyro because it's dynamic. This has been a long, long time coming, and I hope to God they have more input besides Wheelers.
There is also something to be said that the ambitious plan is to return it to performance last seen a decade ago. If that doesn't tell you how neglected PvP has been since the start, nothing will.