If he says so, I see no reason to disbelieve him. I never saw any that I remember, but that doesn't mean they didn't exist. There was a lot stuff supported for those PowerSurge machines which was either never built or built just long enough to discover there was no demand.
For example, according to the Apple Hardware Design Notes, the 7200 can use 256 MB DIMMs. As far as I know no one ever made any 256 MB DIMMs for the 7200 but that would have been kind of cool. It would have taken the RAM capacity to 1 GB, which is very believable, because the 7200 uses the same ROM as the PowerSurge family, and the memory map seems to be largely a function of the ROM.