You are, of course, speculating on what caused Kyocera to abandon the Contax line. I don't beleive the root cuase of Kyocera's pull out was lack of sales. The 645 sold very well and exceeded their expectations for the camera. It is not, obviously, going to sell in the same numbers as a Canon Rebel. but it was profitable (on good margins) and was sufficiently successful that Kyocera designed a new, updated version (the Contax 645 MkII). Even on the 35mm side, they produced some excellent camera like the N1, the RTSIII, the Aria and RX all sold well -- that is, well in their market segment and were profitable.
No, what killed Contax within Kyocera was a lack of effective management and leadership, as well as an inability to understand the dynamics of the technological change going on in the industry and effectively handle to move to digital. The Contax N Digital sold poorly due mostly to gross mismanagement, inept marketing and promotion, and a unwillingness to adapt to much shorter product cycles as technology advanced (old film Contax's had 7-10 year product cycles). All this was true with resepct to the Kyocera brand consumer digicams as well. In the end, Kyocera as a reasonably large company had many balls in the air, and Contax was too small to warrant the management and financial resources necessary to compete. Dealing with Zeiss was a bigconstraint for them as well -- they never really saw eye-to-eye on anything. They, will all the challenges that Contax and digital presented, finally felt their resources would be better applied in other industries (cell phones and cell phone cameras, for example). Quite frankly, they way I see it, ultimately, it was a lack of commitment (and leadership) to Contax from Kyocera's top management that caused them to abandon Contax. In spite of some outstanding products and huge potential in a changing market, the commitment just wasn't there to meet the challenges ahead of them.
If we think about the return of Contax, it's practical to consider what caused Kyocera to abandon the Contax line. It was a lack of sales. If we further consider the return of the line, what's going to fuel an increase in sales; an increase that will be break-even for profitibility? Medium format backs? Not at the current price points. How about shooting film? Get real. Neither is a practical vehicle to return the line to profitibility, at least in comparison to the ease with which most shooters capture with the dSLR's. That's not to say that the dSLR's make better pictures, they don't. dSLR's make smaller pictures that are slightly less sharp because of the low pass filter used to blur aliasing errors. dSLR's have half the image area of a camera back.