@LGB: as you can see from the kernal message, it is not unexpanded, but seems to be maxed out.
I've been digging through the docs of both 65816 and 4510. If the 16 bit features of the SuperCPUs 65816 are used, porting would be rather a rewrite. The 65816 is capable of way more stuff, where as the 4510 is slightly faster running 65sc02 code (the codeset both CPUs can execute).
And to be honest: if I would have to design a computer state at '91 and had to choose one of the 6502 descendants, it would have been the 65816. 4510 would have come in second.