There is no shoe that is perfect for flying any longer...you'd still have to remove it for security

I have a pair of Bass shoes I picked up at its outlet in Galveston a few years back. Not sure what the model/name is, but they are awesome. They are neoprene with rubber soles...basically water shoes...obviously don't fit the TSA profile for secondary screening, but I still have to remove them at almost every airport I fly to/from. They are slip-ons so taking them on and off is very easy. They are also very comfortable and if you remove them in flight and put them back on at the end (after your feet swell), they still fit comfortably.

If your friend is thinking of making shoes, make them out of neoprene and make them slip-ons...neoprene is very stretchy and flexible and people won't have to mess with laces.