Let's say you are correct on Sigma and their lens mount selection years ago....and that it mainly accrued to their third party lens system (which they have dramatically improved), then they continued camera development but never priced their cameras correctly for the obvious desire to pair their much bigger and profitable lens business to it. What sense does that make? Then, they adopt the Foveon, further separating their camera from anything but fixed lenses of Sigma construction(if you assume the interchangeable lenses are mostly designed for film or Sony sensors). Seems a waste of a great technology, which, I guess, they held proprietary interest and unable to compete with Sony or Canon....even through license. I came within a whisker of buying a DP3 Merrill for 400.00 which is close to my limit for camera flings. It's hard to buy a 400 dollar camera than can generate IQ better than FF or sometimes close to MF, especially one that is very portable. the clunky slow AF, the poor zone focus, the bad software.....finally drove me away. However, if your quest is IQ...then Foveon and Sigma are attractive. For 800.00.....there will be FF+ IQ.
Now, if we could only get Ricoh....to build a GXR II....I"d be all in...or an RD1 IV?