The current GooglePlayGames plugin (both C2 and C3) is made for the web API and do not work very well for mobile/android games.
For me personally GooglePlay makes most sense to use in mobile games and not desktop/web games. So to have a GooglePlayGames plugin with support for the mobile API is a must have I think
(In C2 cranberrygames and Coocoon team has their own GooglePlay plugins which works very well for mobile games, using the native GooglePlayGames app for login etcetera, but their plugins lack very much features, such as requesting leaderboard data into the game..).
This is now supported and documented.