The quattro is not a Merrill for those that want the most mega pixels and the original 1-1-1 foveon design.
I still have all four of my Merrill cameras (dp1, 2, 3 and sd1). I mainly use them for landscape work these days.
The dp2 Quattro is my general purpose camera. I am perfectly happy w/ shooting small raw file for my general purpose shooting (5mp - 15mp foveon speak) which allows me to retain the 1-1-1 relationship, since it seems to average the blue layer info into a single piece of info to integrate w/ the single red and green layer receptor below.
The af speed on the Quattro is faster and the high iso is 1 to 2 stops better..the only thing I still don't like is the sd card door design.
If one is after the most mp and still retain the 1-1-1 RGB relationship then the Quattro is not for them..they will be better off w/ the Merrill (so long as they accept the Merrill limitations). The Quattro 4-1-1 algo is IMHO still better than traditional Bayer algo. In certain situations both Merrill and Quattro cameras will show more detail than a 36mp Bayer camera, but on average it is a push.
Whether sigma will ever go back to a true 1-1-1 design depends on not only the market, but how stubborn Sigma CEO is. If they ever did a ff foveon sensor and kept the mp the same as old Merrill, I could c it being possibility, but in apsc, they may have hit a technology wall, which forced them into doing a Quattro style design. Btw the Quattro like patent is less then four years after the basic foveon one (done while mr. Merrill was still alive if I remember correctly).
I am interested in seeing what they plan to do for the sd1 Merrill replacement myself. I might just pull the ir/dust filter off my sd1m to turn it into a full spectrum camera.
Gary