There is: the GRexx PCI that was designed by Phase5. Sadly, I don't think it's supported in OS4 (part of the original red/blue platform split, the GRexx is AFAIK, supported by MOS), or is likely to be in future. I'd love to be wrong about that though. Speaking from a pure hardware perspective, it was a far better solution for the BlizzardPPC than the Mediator1200 IMNSHO.
There was only a very limited amount of these ever produced, besides it wouldn't work on my A4000T. I'm more thinking of a single adapter for connecting the Radeon to the CSPPC expansion bus, but this probably also needs documentation and be expensive to produce.
