Earlier quoted context omitted.
There is too much TimeCube on that WWW site. Try this one. * https://retrocomputing.stackexchange.com/questions/14864/wha...
From skimming the datasheet, it looks like a fairly bad product. Sure the A register is extended to 32 bits, but the 8 bit data bus means that it's not going to be much faster than the 65816 and the address bus is still 24 bits. I have no clue why WDC decided to keep the same pinout as the 65816.
The entire market for this new chip would have been 100% of the people with a 65816 and only those people. Companies do this for a couple reasons, last ditch effort to get cash flow or bridge a gap in a delayed product, extend a product line another cycle, etc.
Pinouts are powerful interfaces (semantically), look at the op-amp, what a wonderful design.
*edit, turns out this chip would have gone in last model of the Apple IIGS but it was the 65816 instead.
I find this stuff fascinating, how technologies fold and morph over time. Esp with MIPS pivoting into RISC-V.