Intel evolved the x86 line beyond 386, into Pentium Pro and then to amd64. Why did Motorolla not do the same with the 68k? I have seen discussion that treats it as assumed knowledge that 68k was obsolete and needed to be replaced by powerpc. But it seems like conjecture - I have not seem technical arguments, and 68k seems like a cleaner architecture to ride forward than post-286 x86.
Sort of. There was the VME bus. An attempt to have a standards based bus that would work across vendors, and also for the the 88k cpu. It wasn't wildly successful, but was mildly successful.