So I guess there isn't a lot of interest in this product, but I find it's open nature rather refreshing. You can put pretty much what you want on it without hacking, though it is a bit involved to compile packages. I'm working on software to make that a bit easier but in the meantime, here are my findings, thus far:
Packaged up UCE files are how you add your own games and they pretty much act just like the included games and show up in the menu in the "addonx" section, which you can configure to be the start up folder. You can make folders on you usb stick to organize your games and they expand and collapse just like the filters for the included games.
USB hubs work fine so you can plug in controllers and usb sticks at the same time.
There are two types of hardware marquees, one lcd and one DMD, that work with the unit and are sent info from the puck via wifi. If the protocol can be worked out, then an open-sourced marquee solution could be built.
The axis of mice are detected out of the box and work in game without configuring anything, so usb spinners, trackballs and mice should work out of the box. This is probably due to the built in aimtrack support. The mice buttons, on the other hand, don't work. If you are adding a trackball or spinner to one of their existing panels this shouldn't be a problem as you can use the joystick buttons, but it does complicate stand-alone controllers.
Plugging in a keyboard exposes all inputs as keyboard keys. They are mapped as follows:
Home Button = M
Rewind Button = R
P1 Start = Enter
P1 Directions = Arrow Keys
P1 A = A
P1 B = B
P1 X = X
P1 Y = Y
P1 LB = T or V
P1 LT = F
P1 RB = H or Z
P1 RT = C or N
P2 Start = Spacebar
P2 Directions = Numpad Arrow Keys
P2 A = F1
P2 B = F8
P2 X = F4
P2 Y = F5
P2 LB = U
P2 LT = J
P2 RB = F6
P2 RT = F3
ESC also seems to work as a back button though it behaves slightly different.
You can navigate the menus and play the games with only a keyboard just fine; the only problem is the system needs to detect one of its supported controllers upon the start of the first game. That's not a big deal if you are trying to make a 2p controller but sucks if you are trying to do something stand alone. My guess is it just needs to detect a usb device with the correct HID and PID which could be easily faked with an arduino but I haven't confirmed that yet.
As I said, more news as it develops.