With MPEG-2 support, these devices will make excellent DVR frontends for US broadcast MPEG-2.
MythTV seems like a no-brainer. The independent backend server is a perfect companion for the Android TV frontend.
Any apps available or planned? Or, are there any other DVR backends that will work well with one of these boxes?
Wait to see if SiliconDust makes one
I personally would rather have a DVR built using Android TV as the OS. But who knows if that will happen. The reason I say this is because some network-based client-server DVR solutions seem to be a bit wonky as far as channel switching, etc. goes. Maybe I'm just being picky, but I've used TiVo + OTA since 2007 and it's hard to beat.
I do believe that when Android TV was demonstrated at Google I/O they were showing a Silicon Dust app which was probably connected to one of their HDHomeRun DVRs. So that may be an option in the future.
XBMC DVR has a plugin for MythTV and many others. It runs perfectly and plays every format too on Android. http://yocontrol.co.uk/kodi-pvr-enigma2/