I am currently working on a .NET Core/Mono integration with QML.

https://github.com/pauldotknopf/net-core-qml

The idea is to only have bindings for QML engine and it's parts, with the ability to use .NET objects (properties, signals, slots, methods) with vice-vera (using dynamic).

It is very much in the early stages, but to me, the idea seems very promising.

Not specificly .NET Core, but Xamarin is already available for macOS and is, afaik, actively working on Xamarin.Forms coming to desktop, including Linux.

We use Eto.Forms for our cross platform dotnet core app.

https://github.com/picoe/Eto