Ashley has alerady said what the solution is to the 50MB. however understand that I don't know how to implement this.
1. In your game. Make sure to check for updates. Some how you can specify a URL.
2. Export your game to XDK.
3. Remove game assets that are not part of the "First install screen". (ie UI, levels, audio).
4. Place the HTML export of your entire game at the URL
5. Pack the XDK GooglePlay version up to XDK compiler system.
6. ??????
7.Profit..
no I'm kidding.
6. Players will download the game.
7. Upon first run the browse for update should go to the full games website.
8. Game should now download all assets.
however. i have not done this myself. But this is Ashley's suggestion for getting around the 50mb barrier.