It would have been the most powerful 8-bit micro, but it was never meant to be as Commodore cancelled it in the early '90s. Still, a few working prototypes of the Commodore 65 or C64DX were crafted and we do now know that this computer would have been something between an Amiga and a C64.
It would have come with a powerful 8-bit custom CPU clocked at 3.54Mhz, a graphics chip that would be able to display 256 colours from a palette of 4096, stereo sound provided by dual SIDs, 128k of RAM, a 3.5" disk drive and a new and vastly improved BASIC. Oh, and it would also sport a C64 emulation mode too and all sorts of other improvements. You can find out more about the C65 here, here and here.
Also and as the wonderful people of Retro Collect discovered, a wonderfully preserved, working and ultra-rare Commodore 65 appeared on eBay. You can bid on it via this Commodore 65 / C64DX / C65 prototype auction. Seller ships worldwide.