I know the main told issue is that the CPU is a surface mounted device (SMD). When I talked to the subject to various pretenders for this job, they always replied that this was a no way issue, but I know sometime (maybe on the Social Entropy (Quicksilver 303/606) forum now deleted) someone brought a technical workaround for it. It was a kind of SMD to thourgh-hole adapter and it seemed to be a way to look into.
The problem here is not so much, that it is impossible to design a CPU replacement for a surface mount part. The way I would probably do it is to design a PCB with edge connections, so it can be soldered directly in place of the original CPU.
The issue here rather is that potential customer (and I believe this even includes some synth techs) are not fit to desolder a 64-pin SMD cpu and solder something equally complex in its place.
From what I have seen some people already have problems with through hole.
Finally I felt that the technical barrier was a pretext to hide the fear that the thought-to-be-a-fact that “the MC-202 is not so popular” would result in a commercial flop.
Given the obstacles of soldering described above, the fear of a commercial flop is not quite unjustified, imho.
See, the first question a developer might ask is: “Is this mod needed? And will it improve the synth significantly?”
But the second question usually is: “If I spent several months of my life developing this, will I get paid?”