OpenLayers
We've chosen to use OpenLayers v2 which is a generic, portable and highly customizable Map API. It has a concept of layers and allows using any map source as a base layer and provides a ton of functionality that can be added as various layers. The next version (Roadmap here) which just released its alpha yesterday will support some very cool WebGL based functionality and tighter integration with projects like Cesium - Demos.
Since I'll be stubbing that API, I was wondering if it'll be a good candidate to be integrated in the Script# project instead of Google Maps?
Would be great to see. Should the library target v2, or the upcoming v3?
Good question. I had inquired about the release date @ https://github.com/openlayers/ol3/issues/633 and it seems like v3 is slated to release around June with potential API changes between now and then.
With that in mind, I'll stub v3 when it's ready. Internally, I'll continue to use v2 in JS.