They are going in the right direction but i feel like they still have a long way to go before people in the Linux/OSX world start taking C# seriously and we see actual products.
Especially with all the hype around containers, C# is left in the cold. The deployment story would have to be as good on Linux for many to even consider production services
I've been able to use several of the onbuild base images with C# projects.. given they weren't anything huge, but it's been pretty cool. Should only get better.