I'm thinking Valve basically wrote off retrogaming with this device - it's after the modern genres that are completely split between the PC-style mouse-and-keyboard and the console-style thumbsticks-and-shoulders.
A retrogaming pad would be nice as an additional peripheral to sell, but realistically you can use any existing bluetooth gamepad with Steam.
Good point: Since it works w/ any gamepad, in theory, you should be able to get a nice bluetooth version of your SNES pad and have it Just Work. If you're already playing those kinds of games, you might already have one for your computer anyway.
A retrogaming pad would be nice as an additional peripheral to sell, but realistically you can use any existing bluetooth gamepad with Steam.