During one of the stand-ups, from maybe last year, a question was asked about "what about 4.x's future?". I don't remember their actual wording, but my takeaway was: Right now it's all-hands-on-deck for .NET Core. It's new and exciting and there is a flurry of activity because of that.
It's expensive and resource intensive to maintain this level of activity. I think you will see things (related to .net core) calm down and the progress won't be much different than what we currently see on the full .net stack.
The .NET World will be a mess if 60% of features are in .NET proper and 60% of features are in .NET Core.
If we are lucky, they will allow substantial outside contributions to the project and that's where we see most of the future development. The biggest hurdle will be to create, and maintain, excitement around .NET Core.
This is an investment by MS, so they need to eventually see some return. My guess is they want to see this return as street-cred (hence the community outreach) and in Azure (which is always mentioned in the first few sentences when describing why they did .NET Core).
.NET-Proper was created to sell windows server -- .Net Core was created to sell Azure. Long live VS!