From what I gather this adapter (the one for the Wii U Pro controller) doesn't just do what a BT dongle and Glovepie or whatever does, it can sync up to 4 Wii U Pro controllers at a time (in Direct Input mode), those controllers will show up as HID devices which can be calibrated and viewed in Windows Gamepad Setup. If it's still HID, then that means my Joy2Key profiles should still work... I might have to swap zL and zR for L and R (since they switched places on the old Wii Pro and the Wii U Pro), though.http://www.youtube.com/watch?v=5VjLI3rNkzk
I'm going to -assume- that this adapter will operate similarly to the wireless adapter for the old Wii Classic Controllers, ie: Controller enters sleep mode, press button to turn it back on, everything is still synced to the adapter. Windows still treats it like any third party USB gamepad.
Xinput I guess is for those games like Bastion that won't let you have access to the Gamepad mode unless you're using a 360 controller (but then I got around that using x360ce (fools the computer into thinking whatever you have hooked up is a 360 pad, in my case the Classic Controller).
Even though the idea might seem superfluous or stupid, I think it's nice that they make these things.