The CPU slot maxes at 128MB.
It's the same with all CPU slot accelerators (Cyberstorm etc).
I seem to remember about 2GB of reserved address space in the A3000T memory map. And what is max that Zorro3 has defined? I don't remember now. Anyway, that PPC can surely address way more memory than what was ever defined by Commodore. What this more likely is, is a PPC system design with address space assigned to the 040 and to the Amiga motherboard.