Collect your battle standards and medallions before they become grandfathered bis items. Recommend to get your legion gear in place, else you won't be able to transmogrify most of it.
Blizz stated already that the vast majority, if not all, PvP Gear from Vanilla > WoD would be purchasable via Gold once Honor/Conquest is removed. That said, it's always better to be safe than fucked, the way Blizz handles things lol.