Похоже, у Авалонии появился конкурент
https://hub.packtpub.com/qml-net-a-new-c-library-for-cross-platform-net-gui-development/
https://hub.packtpub.com/qml-net-a-new-c-library-for-cross-platform-net-gui-development/
Packt Hub
Qml.Net: A new C# library for cross-platform .NET GUI development | Packt Hub
Qml.Net is a new C# library for cross-platform .NET GUI development. It is in its early stages and supports all major operating systems.