But if they don't have the later I/O board they will not be able to use the mini GSU unless they make an adaptor of some kind
I'm might be wrong but I don't think that's true. Earlier ECU version owners can turn around the micro I/O board supplied with the mini GSU. You use a phone cable from the ECU to the phone socket on the micro I/O board. There is then a free Minibridge connector on the I/O board to plug the GSU into.
The only people disadvantaged are those that have a V10 ECU with micro I/O board (as supplied with P20)[&o]