That's why most of the engine producers are working flat out to meet the emissions requirements.
The fuel companies are also striving to clean up the fuels but the biggest problem at the moment seems to be the particulates.
I see an "exemption" coming along in the future.
Also, it would be impractical or unreasonable to backwards enforce this. That big Scania thundering along the M25 could not be forced or required to comply with future legislation.
Afterall, you can't get 4 star leaded fuel anymore, but there's plenty of cars still around that were designed to use it.