I don't think unifying any of this is a good idea.
The pad handlers are emulating cellPad and cellGem (necessary).
The emulated devices in IO settings are cellUsbd (optional since you can have a real device plugged in).
The USB device settings (someone reordered them to make them more confusing) for these only remap the buttons contextually.
Merging any of these would be a total nightmare code-wise and UI-wise at the moment.

The most sensible integration as psmove would be to add a pad handler for the Wiimote and reimplement the ps move orientation functions (if that's even possible with a wiimote) and tweak how to get the screen coordinates in cellGem if the pad is a wiimote.
After all, ps move controllers take the last 4 player slots in cellPad.

But I don't know why this is even a conversation in this unrelated PR.
After all, the guncon has nothing to do with it xD.