High Quality QLED Ulta definitionTVs support 120Hz refresh rates, till now AppleTV was running with 60HZ, The higher refresh rate would allow for sooth playback of video game and action movie content where higher refresh rates are crucial.
While upgrading to new Apple 4K tv with 120Hz refresh rate, you should buy a HDMI 2.1 cable as it supports 120K refresh rates at 4K. Old 2.0 HDMI cables support only 60Hz. many of new Samsung, LG, Vizio tvs support play back at 120Hz.
the next-gen Apple TV will get a high-end A14X processor insted of A12X processor similar to apple 12 line up with console-grade performance for apple's new 30 arcade games.