I've been a (mostly) C# developer for 10 years, and am terribly disappointed with the way .NET Core is being managed. Something is definitely wrong when promises are made to assign a developer to the issue, full-time, and then no communication happens after that, for months. All they needed to do is test and merge the hard work done by a volunteer!
These problems are eclipsed by the the marginal success of the 95-99% of use cases that are covered by .NET Core.
One of the lesser-known areas that C# and .NET has shined, involves plugin and modular development. AppDomains and secure code regions are a feature of the runtime. For more esoteric use cases, the classic .NET runtime itself is customizable, with replaceable COM interfaces using the C++ hosting API. This is how SQL Server implemented stored procedures that could be written with C#.
The way .NET Core has treated the issue is tantamount to a betrayal of trust. I understand that they are trying to take things in a different direction, but doing so undermines the other features that .NET provides, and does so well with. Not to mention they did promise to work on, and merge the feature, before leaving people hanging with no further updates in communication. A cross-platform .NET Core that doesn't have this kind of feature is not going to do much that Python or Java cannot do. We should be far more worried about .NET Core competing with .NET Framework, than .NET Core competing with Mono.
Is Microsoft trying to provide a good tool, to empower developers to build things that could not be easily built before? Or is the primary goal to be seen as friendly to the Open Source Community, by providing yet another dumbed down, cookie cutter cross-platform SDK that deserves no relevance? Are they intentionally omitting or delaying features that one would use in more advanced scenarios, forcing developers to make a choice to use classic .NET Framework (Windows/Mono)?
It is starting to seem like the same old tricks by Microsoft, just more cleverly hidden.