CONFIRMED! Hardware Decoder does work in Android M!
I just installed the Android M Dev Preview on my Nexus Player, and I am able to hardware decode mpeg2 streams.
I have an HDHR3-US running through InstaTV-Pro with the Hardware - Type B Decoder. This did not work in Lollipop, but does work in M! The HDHomerun View app did not work with the older HDHomerun device, but InstaTV does.
I would be happy to answer any questions so AMA!
I flashed M on my nexus player for this functionality a couple of days ago. So far, I'm getting a lot of errors (says something like "HDHomeRun View has stopped working") when using the Live TV app. The channel eventually tunes after the error pops up a couple of times.
Nexus Player + HDHomeRun Prime connected via wifi (getting OTG cable + USB Ethernet dongle tomorrow..hoping that helps)
Some people suggest that the little atom processor in the nexus player isn't strong enough for mpeg2 decoding, even if it has the capability in the software. What's your experience? Is it good or does it suck?
Thanks for investigating and reporting! This is very good news, since the Gizmodo article only mentioned HDHR working on the Shield TV.