I would absolutely love to see a 128 core, but I know I am in rare company. I'm one of the few people who appreciate the VDC.
What I would think should be more realistic? A SuperCPU core maybe?
Yes the VDC properties are nice (though glitch-y), the rest of the 128 architecture is a bit of a mess unfortunately. Building a accurate replica with all the quirks will be a nightmare. And because the Chameleon hardware itself doesn't work on a C128, we kind of try to ignore this topic
A SuperCPU comes up quite often in discussions. However if you look realistically there are only a handful of programs that really use the 16 bit instruction set of the 65816 processor. Most of the SuperCPU titles just want the faster speed that is already covered with the existing turbo functionality. Designing a new core for running just two extra programs is a bit meh.