This is straight from Ned Bunnell's blog (President of Pentax Imaging USA):
"Square sensor and full frame??? Executives in Japan have said we'll release a model this summer that is more advanced than the K20D, and that we have re-started development of the 645D which is expected to be released in 2010. When asked about full frame (meaning 35mm camera body), we commented this would be very difficult in the near future."