Would you rather pay $1500.00 for a nicely spec'd FF DSLR or $1500.00 for a comparable APS-C DSLR? I'd rather spend the money on a FF DSLR. The cost of the sensors is coming down. Isn't the new MF 645D based on the same electronics of the current APS-C K-7? I just don't buy the argument that it will take a lot of new programming or expensive design expertise. There will be some accommodations made to fit the larger FF sensor but I don't see much else. Wasn't the K-Mount originally designed for FF?
Being that the K-Mount in itself is a FF mount, Pentax had to switch to a smaller sensor (APS-C) when the the Philips sensor deal fell through in 2001 or so. APS-C sensors were just a compromise at the time for Pentax to bring out a DSLR. Now FF sensors are coming down in price and up in quality (read up on Sony's rumored new FF sensor coming in the new Nikon D700s {supposed to be as good as the APS-C sensor in the Pentax K-X}, and Samsungs new FF sensor that will be out in the next 12 months).
A new FF K Mount DSLR is bound to bring new D-FA lenses. If Pentax is not bringing out a FF DSLR why hasn't Pentax at least announced or unveiled any new DA lenses? Hoya has been way too quiet.
I never bought heavily into DA lenses because I remember what a flash in the pan the APS film format was in the 1990's (Kodak Advantix, Nikon Pronea, etc.) Almost all of my lenses are FF compatible because I was planning to upgrade to FF.
I don't see APS-C as professional grade regardless of all of the arguments on this forum. If sensor size makes no difference (which it does) why would Pentax bring out the 645D in the first place? A good FF sensor can easily outperform a comparable APS-C sensor.
In closing, Pentax is bound to keep supporting APC-C through less expensive models like the K-7 and the K-X. Plus, I bet Pentax would make any FF DSLR backwardly compatible with APS-C lenses in cropped mode like Nikon does.
I already own a Pentax K100D and Pentax K20D, I see no real reason to upgrade to another APS-C format camera. I'm not looking to buy another APS-C camera, my next camera will be FF.
Bring out a K-Mount FF DSLR camera Pentax. You have a customer here!