You have no idea how slow mono is compared to microsoft .net 
espacilly in cases that matter for us, like large collections and processing these.
I would be happy to see C# in UE4… but i doubt anyone is going trough all this for free. Important is that performance stays the same or better sayed no one should see in the first look this is done via C# because its feels slow.
PS: C# Dev’s will learn C++/11 before a proper Plug-In for UE4 come out 