2600 Heavy Sixer homage styling, complete with black controllers with red buttons, and that sweet white LED Atari logo that was in the video. I want woodgrain.
A variety of built-in classics (River Raid, Frogger, Demon Attack, etc.) along with modern indie game support. We don't need another thing to play Call of Duty on. I want to sit on my couch and play Cave Story or Stardew Valley on an Atari! Maybe something like what Steam Greenlight could have been. Modern retro is a huge deal, and they could take advantage of it. Giving a weekend developer a chance to showcase something built for the system could be great.
Cartridge based like the Switch.
Online shop to buy games through if you don't want physical copies, as well as the option to buy more classics.
Online play for multi-player classics? Playing Joust against randoms could be fun.