Mips is still very much in use, buried deeply into embedded systems where you don't know or care what CPU it is. It doesn't have the mass-market brand appeal that ARM has. ARM has potential for "desktop" compute platforms in that there are high-performance parts planned and coming soon, with desktop style connectivity involved. I'm not aware of anything MIPS like that. (If anyone does, I'd be interested in learning) MIPS would still leave us mostly in hardware limbo, as there are not desktop boards or laptops being made that we could make use of.
IMHO, if AmigaOS moves away from PPC, there are only two destinations that make sense. Either x86-64 or ARM64. Due to the availability of hardware that makes sense for those available or coming...