I'm happy with 21MP. I'd be happy with 18MP. I can pano-stitch my landscapes in portrait-aspect chunks so long as there's little to no movement in the scene, and that gives many more MP. For single frame grabs like events - then 18MP stuff is plenty. The only reason I'd want more MP is for simulating reach with the crop. Maybe I just buy a longer lens instead?
That's my MP rant. For AF - I'd be more than happy if they had the same # of AP points but did two things - made them all X-type, and spread them a fair bit wider. So Canon - if you gimp the AF one more time in the 5D range, I'm afraid I'm probably out.
As for weather sealing, the 5D2 should be made to withstand heavy rain. Landscape shooters / hikers don't need a big-ass portrait grip to add bulk and weight. The 5D2 is a great size for hiking compared to the 1D line, so it should be sealed accordingly. How many out there have been burned by the poor sealing on the 5D2? I know quite a few.
If Canon can address these issues I'll buy two 5DIII. If there's more of the same, then well... the dark side awaits!