That's tricky. Android's success depends heavily on phone vendors, and the vendors -- at least the large ones -- have only bet on Android because Google's control over it is relatively subtle. If Google tries to extract too much money off of Android, you'll see phone manufacturers forking it in a heartbeat.
In the opposite direction, more and more customers want "pure" software and good hardware is increasingly available from many different manufacturers. Nokia arguably has made the best hardware and hardly sold any phones with WP because customers wanted Android. Google knows this and moves more and more parts from AOSP in its proprietary play framework because manufacturers are way more dependent on Android than Google is dependent on any single manufacturer (including Samsung).
But my feeling from having looked at Android 5 (which is apparently superficial) is that Google still try to run fast, but there is not more any very compelling innovation to propose. So quite soon a normal two years old version of Android will be just good enough for manufacturers and users.
Then Android will still be the main player, but it will exist as multiple forks and Google will have to adapt and propose apps compatible with the most successful forks (just like they propose apps on Apple store).
You know, i'm an Android user because of its openness, because of its ability to be forked, but Google practices a kind of lock-in that is very hard to escape. Basically everything they do is technically excellent, plus they end up dominating the underlying platforms.
I don't think Google is going to do that, they don't have to because Ads make them so much money, but they could.