A hypothetical C500 based on the 65816 could have been made, in place of the A500/A1000.
I think C900 was a very good product for the Unix market. I've read opinions/rumors that C= was actually considering buying Zilog outright at the time. The 16 bit Z-8000 and 32 bit Z-80000 that followed it 2 years after were very advanced designs, Z80000 being fully pipelined, though not without troubles and some design flaws at first.
With C= pricing and distribution C900 had the potential to be a winning product. I don't know which reason was given at the time for the cancellation of the C900, I simply cannot see buying Amiga as a reason enough to bin a product that was virtually developed and made for an entirely different market. Well, the usual C= chaos, I guess...