I think a lot of the reason .NET isn't yet used that broadly beyond Windows is as much leftover distrust/paranoia at Microsoft than anything technical. I tried

I think a lot of the reason .NET isn't yet used that broadly beyond Windows is as much leftover distrust/paranoia at Microsoft than anything technical. I tried to get involved in Mono-based Open Source back in the day and it left a lot of lasting sourness at the "Linux community" and how distrustful/paranoid it could be. Despite Mono being open source. Despite however many open patent agreements Microsoft signed. There was so much ugliness and so many people I encountered had a lot of passion for "Never .NET". I hope that changes for the community. .NET doesn't get any more Open Source today. There's no longer a .NET/Mono split, they've merged. The open patent agreements with the .NET Foundation and other stewardship orgs are about as rock solid as they can possibly get. I cynically saw so much "Never .NET" hate in that community that I can't imagine it won't linger for long past its expiration date.