Official Blizzard Quote:
Did we not already talk about that? Think we did. Like the cap raises another five every difficulty level? So when you reach hell difficulty the caps would be at 15? No? Did we not say that at the last BlizzCon? Think we did.
We also got some information on what Blizzard will be talking about at Blizzcon. It appears that the unique resource system for each character is still being ironed out but Bashiok commented that more information about each system will be talked about at this year's Blizzcon. For more information about what will be covered at Blizzcon and some more answers from Bashiok check out Airandius thread about Core Issues.
Official Blizzard Quote:
Fury is going through some further iteration. The orb system wasn't really working out like we had hoped and was creating some roadblocks. The other resource systems, nothing really to share. The wizard instability is reworked as well. More about all those at BlizzCon.
What potential benefits and problems do you see with skill caps raising with difficulty?
Blizzard's already mentioned (can't remember where) that "rushing" is an acceptable form of play. They have no problem with people helping their friends through the game. However, that's not saying that they possibly won't implement quest/skill bonuses that you lose out on if you get "rushed" instead of playing through normally.
Official Blizzard Quote:
Ignore everything I said about raising skill caps, that was an old, old design for how it could potentially work and I had a lapse of memory.
My money is on the latter :/.