I would venture it's a ton easier to find Java programmers than C# ones (at the current moment), and the same story for libraries for likely the same underlying reason.

As a pragmatic issue, if you weren't already using Mono, then it would probably be wise to let the newly open-sourced CoreCLR stew for a while to find subtle kinks introduced by the process through which it was open-sourced and/or the pressures exerted upon it by full-time dev or test (or even prod!) usage on non-Windows platforms.

As a much more subjective issue, Intellij versus every C# editor is an unfair matchup. It's possible JetBrains will get into the C# editor space now that they might have more marketshare who are not on Windows, but it's probably very far down their priority queue.