Pretty confident that people will be working towards capping out on week one. I see the majority of players zerging fates, much like they did when the game first launched, to get to 60 as fast as possible. Remember the +50% xp is based on your highest level. This way after they get to 60 they can go back and do all the story quests to unlock expert and start gathering the new tomestones, or go back to level other jobs. While everyone is zerging fates it seems to make sense to join them. Given that fate grinding is the fastest way to level.
This also makes me wonder about the current poetics weekly cap. Like you said, the expansion is the likely place for a new tomestone. If true, then still having a weekly cap up until the expansion makes little sense. Especially so if the loot lockout is removed from WoD.
