I will certainly be looking at how this body performs before rushing to buy it. I am very happy with my 645D. A little more resolution, further improved high ISO performance, quicker read/write speeds, etc. are all well and good, but the overall IQ will have to be clearly improved before I spend significant money. What will colour response and DR be like? What about noise at base ISO? The 'character' of the files?
I do feel that 40MP is not enough sometimes, but 50MP is not much of a jump. And the other benefits... jury's still out in my book. I want to love it though and will be carefully watching it, wanting to want it!
The best thing about this is the commitment it shows to the Pentax MF product line!