I'm expecting their Blizzcon announcement to be details of the Arena rebalancing they've been talking about.
I do think they need more modes and features, but I suspect they won't roll those out until they feel they're happy with how the existing content works.
They've addressed the regular mode with rotating sets and ranked rewards, and they've addressed Adventures by giving out 45 cards, much more unique content, and a more accessible price. That leaves Arena as the prime target for polishing up.
I would love a shakeup of the Arena format. I don't know what form that would take, but there are lots of cool ideas out there. I have played sealed draft formats for other card games, L5R, Magic. Arena is similar to how those work, but I'm sure there are ways to do interesting things with it.
Generally the sealed formats I've played only ever involve 1 set at a time which very frequently leads to interesting meta choices. Cards that kind of suck get to shine because there simply is no other choice. I wonder if they will attempt to make a more limited Arena format. Either pulling out the Wild choices or do something more drastic like re-assigning rarities to a lot of the more powerful arena cards.