Technically. The Avalonia team is much more innovative and understand MSFT technology better than the UWP team, clearly. Of course, that doesn't really say much as pretty much anyone understands MSFT technology better than the UWP group. This is one of the reasons why Xamarin was such an attractive acquisition. To date, it truly feels as if the UWP "leadership" has done everything they can to make UWP a product that no one wants to use, for the past five years. Can you imagine getting paid for five years for basically doing nothing? That's the sort of cushy job you would have on the UWP team. In addition to essentially not doing anything for five years, the group is mired in secrecy, closed-source thinking (when everyone today is open-source), politics, and terrible developer relations/engagement. It is in serious need of a reboot.
However, UWP still provides value as its offering is two fold: that of its client application model (which I just got done explaining is not very good at all), and that of its rendering pipeline (infrastructure).
What is useful out of UWP is its rendering pipeline, and that's where its value lies. Again (as I mentioned in another thread), UWP can be considered part of the necessary infrastructure (road) while Avalonia can be seen as the vehicle (car) on which it depends on the infrastructure to operate properly. So, when I mention UWP, I am referencing its rendering pipeline (infrastructure/road) in particular, as its client application model (car) is incredibly, laughably inadequate.
Five years? The good news is that the light is at the end of the tunnel here.
I sure hope so. It is possible that they can also create their own Avalonia, that is, a cross-platform UWP that has a much improved Xaml model and -- well, everything else. I am doubtful on this though because they have been sitting on the same featureset for 5 years now without much improvement (see: cushy job).
And if so, why doesn't Microsoft just open source Silverlight and provide a pathway to Silverlight deployment through web assembly? Or, port the Silverlight graphics library to .NET Core?
As much as I loved Silverlight, this might be a lost cause. But who knows. It might be possible if you get the right community effort around it. I would rather see something new from scratch that tries to capture its spirit. Much like the great work done from the ASP.NET team (a group that does NOT have cushy jobs -- they work their butts off) around ASP.NET Core.
Btw, it's super great to see someone sharing as much enthusiasm around this topic as I do. Seems like people like us used to be everywhere, but now seems that we're all too rare an occurence these days.