I was wondering if some one thought about widening the bus for the 6510 processor.
Eight bit opcode and an eight bit or 16 bit operand for a fpga c64 sound interesting.
There is already a *real* 16 bit replacement for the 6510, the WDC 65816, designed by Bill Mensch, one of the original 6510 designers. It was available from 1984, and has been used in the Apple IIgs for example, and is still manufactured as well as possible to license as a core for ASICs. There's also a drop-inc 6502 compatible version, the 65802, but that's more limited for obvious reasons (no wider external bus)
Since there's been accelerators for the C64 using it too, I'm sure someone will do an FPGA version eventually if there isn't one already.