I feel like somebody asked Bill Mensch about a 32-bit 65816 and he just s/16/32/g. Nowadays, I believe his 32-bit advice is to just use ARM.

The Renesas 7700 took the 65816, stripped out some stuff, added some stuff, and used the WDM instruction as a prefix to enable a second B accumulator.

I remember when the WDC homepage featured a big Terbium section trying to build hype for a 32-bit CPU. I got so excited over the idea at first but it clearly wasn't going anywhere. ARM has done a great job filling that niche in the meantime.