Comment Amazon forked it just fine. (Score 1) 241
But they built their own app store. Microsoft is free to do it as well. Yandex just released kit for using their services and app store too http://techcrunch.com/2014/02/19/yandex-kit/ , so if Yandex can do it, so can Microsoft.
Now, if they want access to Google Play Store they will probably have to go through the same process as any other Android phone vendor and sign and agreement and go through testing and certification. Virgin developers or not, if you want to access Play Store you need an agreement.