Android M Minimum Hardware Requirements

I'm wondering what are the minimum hardware requirements for Android M. Google announced the latest version of Android at IO 2015 conference, but did not mention the release date or hardware requirements. It's not clear which of the existing phones will be able to run the new version.

Of course, all the latest smartphones released in 2014, 2015 should be able to upgrade to Android M; but I'd need some official information. As of now, there's no mention of Android M on official android website.

I'm wondering if we should build a list of phones that will receive Android M upgrade. Shall we?