I can easily see them introducing a weapon forging system. Eg: we've been using ancient weapons of power so far, which is all well and good, but now it's time to forge a new legendary weapon for a new age, crafted by the greatest smiths of our time, and something you can continue to reforge into an ever more powerful weapon as you gather rarer resources in your adventures. That still allows for the artifact power system and customization options to carry over, but in a way that starting from scratch on leveling a new weapon makes sense.
As for class halls, I was wondering this too. I only play a Druid so I'd love to hear from other classes on this, but there is LOADS of free unused space in the Dreamgrove (mostly to the north). It made me wonder if that was deliberate for future expansions to build upon. Because it's the perfect place for player housing to be implemented if it's ever going to happen, and gives us something else to customize (even more than our weapons). And man, the amount of time I'd happily spend hunting down new furnishings... And if I could scatter all my pets around my Druid tree home... <3