Seems to me its more on the people who solve hard problems than on the current crop of .NET developers - if you are writing a complex game/MMO, AI system or what have you, and you choose to do so in Java, C++ or similar when C# might be the better option, the faults on you not the .NET community.
If the whole pool of developers world wide was considered as a big pie, and a certain section of that do these 'hard problems', the solution is to market to them the strengths of .NET. Advocating other parts of the pie who build enterprise apps and who already use .NET that they should suddenly start writing actor systems 'for the good of the framework's OSS cred' seems silly.
As well as a tonne of games in general, which I'd argue are 'hard problems' as well. Pillars of Eternity, Endless Legend etc. Though of course none of those are OSS. Would be nice if at least parts of them were as it would certainly help indie game devs like me :)
If the whole pool of developers world wide was considered as a big pie, and a certain section of that do these 'hard problems', the solution is to market to them the strengths of .NET. Advocating other parts of the pie who build enterprise apps and who already use .NET that they should suddenly start writing actor systems 'for the good of the framework's OSS cred' seems silly.