[cathartes]

Kurzweil Music Systems produced the 150 additive synthesizer around the same time that also used a 12 MHz 68k. Do you know if this faster variant was encumbered in some way that made it less suitable for use in a "general purpose" computer, or was it simply a cost consideration?

[DashRattlesnake]

I'm not sure how you think it would be encumbered, but from the Wikipedia page, my guess is it was mostly cost. The faster variants (like 12 Mhz) were only available later, and I would guess that was due to improved production processes and binning that enabled them.

https://en.wikipedia.org/wiki/Motorola_68000