> Maybe my memory is mixing this up with the Efika512x announcements.

Could be. I don't remember if the RAM amount was part of the announcement, but yes, the MPC5121e can address at least 1 GiB RAM.

> the show stopper "cache coherency" wouldn't have been too much of an issue
> for MorphOS AFAIK

Support for cache-incoherent SoCs was added with MorphOS 3.8 for the PPC460EX, so I think that yes, this support could as well have been implemented years before for the MPC5121e.