First off, I just want to say what an INCREDIBLE and informative thread this is! Wow. I just read all 70 posts and I am seriously overloaded with all the information contained in this thread.
@justinmchase - I appreciate you moving on, but I wouldn't say there's a general recommendation to abandon Xaml. Xaml is alive and well in every major MSFT group except for ASP.NET (and this should be fixed, LOL). Xaml is also very much alive in Xamarin as well.
However, I do feel your pain when it comes to cross-platform/web-based Xaml.
In any case, I would definitely say with 70 (really amazing) posts on this topic, there is definitely a need for a consistent, ubiquitous cross-platform .NET client application model that works not only in compiled (native) runtimes, but also transpiles into HTML5-compliant artifacts and works on websites as well. Something that hits EVERYTHING. And no, it's not impossible. It will just take some time.
Having a unified, official cross-platform library for Xaml serialization would be awesome, too.
Perspex / OmniXaml / Noesis have all got my attention. I was unaware of any of these until today. EmptyKeys is also cool, too.
Anyways, great thread. Really enjoyed the read.