I am more excited about WinUI Reactor than anything else. the gap between Compose/React thinking and XAML thinking is enormous, and Reactor just bridges it. I am curious about interoperability - how would one include a Reactor-based component into existing WinUI 3 app? how would one include a XAML-based control from some other library into a (future) modern WinUI Reactor app?

Don't be, if the WinUI team past performance is anything to come by.

They will leave it half baked like everything else since Project Reunion was announced in 2020.