We WILL have to use binding to make push work. Fortunately Xamarin maintains those bindings for us. If we go off on our own then it means we will have to limit the Android SDK to versions of push that Xamarin supports so that we won't have to maintain our own copy of the Xamairn bindings for starters.

To make bindings work we will have to align our APIs in every binded platform so that the work for writing the bridges is minimized. Align our dependencies and their versions so that they all work on Xamarin, and incur the HUGE maintenance cost of minor changes breaking Xamarin as well as the maintenance costs of of projects being limited to what Xamarin supports (which is usually several months behind what the current versions are). This is a nightmare.

I am speaking from experience within the last year : Xamarin bindings are a pain in the ass. They make the project nearly unusable and are misery given the form of code.