I highly doubt that someone has all classes in full i90 so most people would still do CT to fill in the gaps for their alts while waiting for their i90 to drop.
As for completion, I would give it a week or two before anyone says that they've beaten Extreme primals, CT, HM dungeons and the new dungeon as well. But I dont think people will stop playing just because theyve cleared it.
PvP could be fun for all we know and thats usually the selling point of every other MMO. We will have to see next week!