Of course, there have been bumps in the road in the compatibility story between the two XAML environments. .NET Standard 2.0 will help a ton (in the very near future), deeply increasing the amount of .NET code that can be shared between the environments. XAML Standard 1.0 (in the slightly further future) will help a lot, in particular the fact that Xamarin.Forms is planning to implement a WPF renderer for sharing a much larger portion of XAML across every platform.