Most other EU countries already have pretty tight rules on modified cars. The UK has always had a place for car enthusiasts and a long history of custom cars.
Laws like this do threaten our hobby but it's the minority of idiots that bolt things on that fall off again or cause an accident or make a general nuisance of themselves and we all get to suffer for it.
It won't be the first silly unworkable ill thought out law to come out of legislature either!