Any reason why? From what I understand all regions/pads use the same hardware. While SLC/SLCCMPT/MLC are encrypted this should be decryptable with the OTP that is accessible. Then possible to reencrypt with other console OTP. While the processor requires Nintendo signed code, as long as this is just firmware from another region it should already be signed. Unless there is some other specific thing used in OTP/SEEPROM to lock out based on firmware? Maybe a tool could be made to auto switch regions based on inputting the correct files.I don't believe that's currently possible.
Also, wii u gamepad firmware from what I have read from years ago the firmware is unencrypted on SPI chip. Combined with same hardware any reason why this wouldn't work?
I would love to try this stuff, but obviously don't want to buy another system if this isn't even possible to work.