Microsoft here sounds extremely hesitant to ever do the ".NET Framework 5.0" release that would break the .NET Framework world necessary to push a new CLR Runtime out. .NET Framework 3.x and .NET 4.x have all still been using the CLR 2.0 (for the most part), and the risk at upgrading the CLR is far greater than the .NET Framework 1.0 to .NET Framework 2.0 era. (Certainly the "reward" of the new mostly performance-oriented features in .NET Standard 2.1 doesn't seem worth it at first glance, not compared to the CLR 2.0 upgrade for generics.)