I remember last autumn when I was out jogging. I was listening to an episode of a well known podcast on programming and the future of .NET was discussed. The hosts and the guest on the show were discussing the role of .NET Core and I remember that they recommended using Core for green field projects, and even older projects with a lot of active development. However, they were all very convinced that the original .NET Framework would be actively developed and maintained for many many years to come, no, need to worry. It seems that they were wrong.
Today, the future of .NET Framework has taken a different turn. You probably know that a new version of the C# language is to be released later this year. The new version will be called C# 8 (current version is 7.3). C# 8 will introduce language support for new types that have been added to .NET Standard 2.1.
Here comes the interesting part. In order to support these new types fully, changes are required to the .NET runtime. It has however been decided that these changes will not be done to the .NET Framework. It will stay on .NET Standard 2.0. Only .NET Core 3.0 will support .NET Standard 2.1.
This also means that it will not be possible to compile C# 8 code if targeting .NET Framework. Not even with the newest .NET Framework 4.8 version.
It has also been announced that version 4.8 will be the last version of the original .NET Framework. After that, and after .NET Core 3, the plan is to release .NET 5 in year 2020. .NET 5 will however be based on .NET Core 3 and Mono.
My view on this is that it is probably the right path forward for .NET. The current situation, with .NET Framework, .NET Core, Mono, etc. is confusing for developers, and I am sure it takes a lot of energy and resources to maintain all different tracks.
To you .NET developers out there I would recommend starting to investigating what it would take to migrate your active projects to .NET Core.
You can find an official statement to back up claims in this post at https://devblogs.microsoft.com/dotnet/building-c-8-0/