The difference between FF and digital MF is actually quite large. The 44x33 sensor is 1.68 times the size of a 24x36 size sensor. For small prints it's not huge, but big prints it starts making a difference.
Also, keep in mind, resolution is dictated by lens and sensor/film size. I think we've gotten to practical limits of resolution for APS-C, and we're close with FF sensors. Higher MP sensors in the future will be more of a difference on MF than FF or APS-C. Also, with the exception of the latest generation of the 25mm, everything is still compatible with film, so there's room to grow.
If the next generation sensor came out from Sony, and was 40x50mm or even a full 42mmx56mm, Pentax really could slap the sensor in the next 645D camera, and more or less have everything work.
---------- Post added 04-21-14 at 08:50 AM ----------
Woops-- I've been back and forth between here and the 645Z thread. Sorry for the FF dissing =/.
I'd love an FF, too-- but I think an APS-C, and a digital MF like the Pentax would be the perfect one two punch...
... With a Q in the pocket to capture every situation
I'm glad I don't have the $$$ to feed my addiction with digital gear.... I'm in enough trouble as it is with all my film gear, hehe.