I agree that numbers sell cameras for the first time buyers. However, it's specific features which sell the pro/semi-pro on a body - and thats only after they realize the system has what they need to do the work they require.
I'd therefore say skip the next body until the road-map has been realized to a further degree than it has been so far. Get the lenses and accessories into the stores and that will increase sales right there.
For the next body - when it does come, I hope they keep to the same philosophy as they did with the K10D. The K10D is better suited to outdoor photography than any other camera in it's price-range and if they keep that in mind in the next body, I think they're going to continue with good sales figures.
As for my wish-list, I won't bother putting it all down here as it would make for a long list that probably wouldn't suit most shooters, but I think a a few things need to happen in a general sense if they wan't to keep up the momentum:
More fps: It's expected because thats what the competition is doing. 6 would be a good start for that, but no more than that as SD cards only have so much room.
More MP's: Token upgrades will raise interest, but only if they can deliver on better dynamic range, improved noise and maintain a useful range of ISO's (and take it one step further....ISO 25).
Faster AF: It's time. It's well past time for a boost in the AF department - even if it's only for SDM lenses. It's one of the sore points with people looking at Pentax and it's a reason for dismissing them. No matter how fast it might actually be, Pentax is battling perception; simple as that. This would require making/bringing to market a cheap kit lens with SDM so the regulars get a taste for it too.
Make it quieter: Dampen the mirror slap and keep the camera's noise to a minimum.
Ergonomics: You're never going to please everyone, but my MZ-S is king in this department. Even the DS2 was amazing in terms of the grip used. The K10D was a step backwards, AFAIC.
While on the topic of the MZ-S: Lets have that magnesium alloy body back. I've got no doubt that poly-carbonates are strong and durable. I still like metal....and a canted top plate too.
Flash sync: Another point that makes people look away. Up the speed to 1/250. Makes little real-world difference, but it will please the masses to some degree.
Flash sync terminal: Add one!!!
One up the K10D: Along with weather seals, a bit of shock resistance would be a nice boon.
There's a slew of specifics that I could get into, I think those points would be the best places to start.