In a change from last year, Google officially plans to update the M Developer Preview at least twice before final release.
Speaking at the "What's new in Android?" talk at Google I/O, Chet Haase of Google explained how the Android team plans to update the latest Developer Preview. Unlike the L Developer Preview last year, Google has an upgrade path set up to update the M Developer Preview once at the end of June and again at the end of July, each time integrating changes based on feedback from developers.
Those updates will lead up to the final shipping release of Android M in the Fall, and provided everything goes to plan those updated Developer Previews will be great building blocks for both developers creating apps and Google as it works on the final software.
You can catch a full replay of the session, which gives a very quick overview of the M Developer Preview from a perspective of developers, right here.