[wrxtasy]

Have a read of this rundown of Android TV - Live Channels - Nougat 7.0 integration.

Live Channels Updated, Supports USB Tuners and Adds DVR Capabilities

I would basically expect a list of relatively cheap, compatible, ATSC (to start with) USB Tuners to be Plug N Play compatible with Nougat and the Shield. Then the integrated Live Channels App on the Shield should be able to timeshift and schedule / playback recordings from a directly connected or possibly Networked HDD.
Some sort of Tuner config setup, either via Nougat Firmware or via the Live Channels, or similar App itself will have to be added as well.