This is true that Rosetta is a JIT, but my point was more that the Mach-O binary format allows for multiple architecture binaries, therefore somewhat obviating

This is true that Rosetta is a JIT, but my point was more that the Mach-O binary format allows for multiple architecture binaries, therefore somewhat obviating the need for a jit. The only use Rosetta served was running cross architecture binaries. Mono also doesn't run the full .NET stack, e.g. think the Netflix drm components, so I can't quite consider it cross platform. Cross platform windows wise sure, but that isn't saying much.