Evolving platforms is difficult. Breaking changes in particular are challenge.
Naming is also a challenge. A big challenge.
Google moved from Angular.js to Angular 2.0 to just "Angular" (version 4, skipping 3).
Good look searching for compatible code.
Microsoft's ASP.NET is based on .NET (1, 2, 3, 4... )
ASP.NET Core 1.x is based on .NET Core as well as on .NET 4.x.
Now ASP.NET 2.x is based on only .NET Core 2.0.
So switch to .NET Core one must, period.
At least it will be fast, and there i a good reason for calling it 2.0, it is a breaking change.
ASP.NET Core 2.0 Drops Support for .NET Framework 4.x @InfoQ
ASP.NET Core 2 Preview Released @InfoQ
BUILD 2017 Conference Rollup for .NET Developers - Scott Hanselman
Introducing ASP.NET Core 2.0 | Build 2017 | Channel 9
Managing dotnet Core 2.0 and dotnet Core 1.x versioned SDKs on the same machine - Scott Hanselman