They ought to stick with a level 20 cap at first, with annual expansions. that way each expansion could actually bring new content without overdoing the gear just before the expansion.
With any other company, I'd be hesitant to even look at a new MMO, but with Blizzard, I can hardly wait. They can't very well improve the look and graphics engine with WoW because WoW has a certain look to it. To upgrade the look would mess up the flavor of the World of Warcraft. With a new MMO, not based off anything they've done before, they can go more realistic and do things that other companies haven't been able to pull off.
I played EQ for years before WoW came out, and I've always considered WoW to be everything EQ should have been: easy solo play, listening to their customers, more customizable interface, fixing bugs, a good PTR system before releasing their patches, actual news before the patches came out for testing, etc. EQ had failed so many ways, and Blizzard did everything right with WoW. That's why they have 13 million players. They listen to and communicate with their customers. Most other gaming companies don't come close to doing that.
This new game ought to be great.