If you want to resurrect an old project how about the G3 PPC card instead?
For AOS4/MOS?
Yes, there are dirt cheap PPC accelerators out there for old Macs but it will never happen for Classic Amigas because Hyperion will probably never sanction such a project. It would be too big ofa a threat to the Acube and A-eon partnership.
As to MOS, that should be discussed with the MOS team but I doubt they would sanction it either.
So, pretty much the only choice now for classics is either 68K(OS 3.x) or Coldfire(AROS68K) acc boards.