Basically it seems that Google has plans for two developer preview updates before the final release of Android M to the masses. The first developer preview update has been pegged for a release towards the end of June, and the second one is expected to be released towards the end of July, meaning that we can look forward to Android M’s official and final release sometime after that.
Granted this isn’t exactly a specific date either, but it gives us something to count down towards. Naturally all of this is barring any issues Google has with the release, so if something breaking or major pops up, you can bet that they will be pulling back its release date, but if everything goes according to plane, after July would be a good bet for Android M’s release.
So far Android M appears to be an update focused more towards the performance of Android and less about its aesthetics. Google will be focusing on improving battery management, handling of app permissions, mobile browsing, as well as introducing new features such as Android Pay and a native fingerprint security API.