One can't pick out just one element of say US airspace management and transplant it over here.
The US model works because they have a lot of Class E, in which you have to be VMC unless you have an IR and are on an IFR clearance, but they at the same time they have always had a very accessible IR, approach controllers who don't invoice anybody for the service, no Class A below 18000ft, easy CAS transits which are mostly enshrined in law and not subject to which side of the bed the ATCO got off, and finally they do enforce transgressions. Plus they mandate Mode C transponders around big airports. Plus the FAA designs instrument approaches for airports, for free. The whole lot hangs together.
The question is what can be learnt over here which is politically possible to implement.
Not a lot...
One could start with the IR. Over the 10+ years I've been flying, an easier IR has been "just around the corner". Now there is an EASA one "just around the corner" but not deliverable before they first screw most of the private and sub-airline commercial pilots who have IRs already, in a blatent finger-up to the USA. The whole thing is wrapped up in stupid Euro-superior and anti-US politics.
A change of Planning regs to enable the establishment of GA airfields away from towns etc. without creating a risk of them being converted into housing etc. Very hard to do politically and would require real vision, which doesn't exist in UK Govt.
Airspace redesign is another thing but also very hard politically.
Etc.