Understandable, but still a little disappointing. If this OSS initiative is worth anything, the platforms need to be at parity for features and release.
I'm currently working on Roslyn CoreCLR and cross-plat and Mono is working on integrating more of Roslyn into their stuff, but I don't think the two are necessarily connected, so I wouldn't strictly describe the two as duals.
Note: Only works on Windows right now, going to get to Linux/Mac ASAP :)