Update August 2019: Added tags to the project templates and target files for older .NET Micro Framework versions.
This time just quickly, no code...
I managed to update most of the .NET Micro Framework SDK code to compile under Visual Studio 2019, however the final VSIX generation step will likely require non-trivial changes that are currently above my time constraints. I succeeded however in editing the existing VSIX manually so that it works with Visual Studio 2019. The SDK has not changed, so if you have it, you just need the VSIX with templates.
In order to use versions 3.0 to 4.3 of the framework, you will need to install the .NET Micro Framework 4.3 SDK too, in addition to the 4.4 version above.