Miguel move is for get some windows developers to GNOME and to try to get momentum to compete with KDE.
Unfortunately, M$ don't understand about standards and will try to tie C# to Windows (remember Java)?
Very soon, C# versions become incompatible but M$ will use GNOME to bless its nobody-develop platform C#. And better than all, OpenSource community will waste time going **behind** microsoft goes, as Miguel said.
I dont hate M$ and believe that some efforts as Samba are good because smb is one facto standard, but who are using C#?.
Want to get a new multi-platform environment?.
Use Java then, but Miguel don't want this because Java can run in KDE too and there is no advantage there.
Want to do a fresh aproach to use multiple language and platform in one standard way?
Create your own standard (Call it D++) and do it as superset of Java and C#.
GNOME did a bad choice in its fundation and that was to be based in C. Using any platform (C#, Java or any) will be a very bad idea. Use C++ as KDE does.
Don't put the dust under the carpet.
May be i'm wrong but, if C# succeeds then KDE team will be in better position to extend its functionality because port from C++ to C# is far straigtforward than C to C#.
Anyway, GNOME will lose.