Aren't we all just kinda dancing around in circles here?
I mean, everybody knows that .NET is (for all practical purposes) a Windows-only (*) (and, in fact, MS-only) thing. Yes, there is Mono, but everybody knows that's a joke. I think that we will eventually find out that Mono is actually MS-funded: a sinister plot to ward off the monopoly claims against MS. That is, MS does actually have a legal interest in maintaining the fiction that it has competition. Plausible deniability, and all that...
Based on what I know about .NET, I find it highly unlikely (**) that a .NET app developed on and for Windows would be anything approaching directly portable (that is, retaining the look-and-feel of the original app) to Linux. For one thing, the mental model of the Windows GUI is completely different than that of the Unix/Linux "X" GUI.
(*) Yes, insert usual comments about "But, but, but. Windows runs on ARM" here.
(**) And comments I've seen on various forums back me up on this.
And some folks need to stop being fanboys and see the forest behind the trees.
(One of the best lines I've seen on this board lately)