One of the most exciting news at this years //Build/ conference was Microsofts commitment to Universal Apps. One binary and one store for all Windows 10 devices available, ranging from a Rasberry Pi to Xbox.
This did however raise a concert from my part. What will the integration with Xamarin and specifically Xamarin Forms look like?
The way I would most probably suggest, knowing what I know today, is to create a Xamarin Forms project but drop the Windows Phone project and create a universal project to represent the windows platform. You might want to keep the WP project if you want to support WP 8.0 (silverlight) though.
I would also use a Mvvm-framework, like MvvmCross or MvvmLight to share ViewModels between all projects. I still think MVVM is the way to go to achive the most code share possible.
It's also going to be interesting to see what Xamarin Forms for Windows is going to target in the end.
Bottom line, it looks like you are going to have build two sets of UIs from now on...