It would have been great if it allowed to make .NET Desktop apps for macOS and Linux, in addition to Windows.
I'm really rooting for the project to gain some support. Right now I'd love to try porting our custom UI component at work to Avalonia, just to try it out. But that's time not well invested in something with little backing and potentially few customers for us.
I am not the biggest fan of HTML, but considering the maturity of that ecosystem, design tools and knowledge among designers, that could be a very valid move.