The new XAML Standard is a really exciting development for us as developers working with WPF, UWP, and Xamarin. We are monitoring the development of the standard very closely to determine when it provides sufficient functionality and platform support that would make it possible to transition the APIs included within ArcGIS Runtime SDK for .NET over to the standard. We also need to consider what that transition would mean for users building apps today with our API (upgrade experience, breaking changes, etc).
The goals of the standard are quite vague, however it doesn't seem to have any effect on the ArcGIS Runtime what-so-ever, since its goal is merely to create a standard set of vocabulary among the different XAML flavors when interpreting the XAML (like a TextBlock is called a TextBlock and not a Label, although under the covers it's still a Label). As such this won't really have any effect on the runtime. Also we already use a standard vocabulary so in a way we are a little bit ahead of the standard (ie it's always called a MapView, and it always has a Map property etc on all the platforms we support).
There wouldn't be any changes required on our part - it'll just come to you for free.
Having said that, I'm personally taking an active role in helping to shape the direction of the standard to ensure it'll fit the needs of our customers and the pain points they are dealing with. I'd encourage you to do the same, as the standard is being developed in the open.