it would require an entirely new rendering engine too; the Moho Engine draws with DirectX, and there's no DirectX API on the PS3.
It's a more complex issue than that, actually. Game developers often write their renderers in a proprietary API that compiles into a platform specific API. No doubt a lot of work would be required however the API is written, but it is difficult to accurately estimate how much.
Though I also suspect that rewriting the renderer would be the least of their worries.
Getting the engine to run
on the PS3's cell processor is surely easier than it sounds, as the engine has already been shown to compile on a PPC-based processor. Getting it to run well