Particularly if it means there could be one platform on which to write apps for both WP7 and Android.
I doubt Ballmer would go for it. He probably still thinks "Linux is a cancer" and a threat to be destroyed, whereas in fact the threat to MS is more from Apple.
If I was running MS I'd use the disquiet Oracle has created in the Java world by pushing for .NET/C# to replace Java as the standard OS-neutral run-anywhere platform.
Personally, I wouldn't touch Mono would a ten foot pole, but that's just me....
For exactly this reason, I don't expect to see this happen.
While I'd love to see some funding for these awesome guys, I don't think that Microsoft's money would be that great. Moving Mono development from a big corporation to a small startup might even help settle some of the FUD problems. Receiving money from MS probably wouldn't...