I think VOSA (Government) will have something up their sleeve being developed in the background to achieve this, be that forcing mainstream companies to give up Customer Databases, or impounding suspect cars and forcing you to prove via RR tests, they will be able to have an fair accurate educated guess, brakes, susp, Intakes, exhausts , even go-faster stickers plastered all over the engine etc.
Then it will be up to you to prove a lack of mapping.
I wouldn't be overly concerned though, lots of friendly MOT testers.