Using XAML for my own UI framework

So, this might be somewhat off topic, but I'm trying to find places where people in the know might have a view on this. I've used WPF for many years (10+) but now do VR development in Unity. I'd like to adopt a XAML based markup language for my own UI system (for procedurally building 3D UIs in Unity) and am not sure how to approach this. Ideally I'd like to leverage support in the .NET framework or elsewhere to do the heavy lifting going from my markup/UI types using XAML ->my object graph but don't know where sensible to start. Clearly XAML as markup is used by more than WPF, so should be extensible - but how? Does anyone have any advice or can propose a good resource to look at.

Also, the level of support Unity exposes could also be an issue in implementing any suggestion.

Thanks.