With it using Open Source code and using USB for the controller connectors, I can guarantee this will be hacked and booting external ROM's on day one which would drive sales quite a lot.
I doubt it will be long until someone adds support for generic controllers too. My memories of trying to navigate 3D worlds with that painful d-pad on the pre-DualAnalog/Shock PS1 controllers are not particularly fond ones, though I'm assuming the games list was selected with this in mind.
Kinda ironic really, especially if you were around in the Bleem! days. Where Sony did absolutely everything they could (even illegally at times) to stop it being sold. And succeeded.