I've never installed a charging point and unfamiliar with accepted practice, but I can say with certainty that no 7kVA wirewound transformer ever mounted on a DIN rail. It will be in the order of 50-60kg and the size of a case of wine unenclosed. This is due to physical limitations of the copper and steel, and until someone invents a revolutionary material with better properties, it won't change much. It is possible to make a smaller, lighter switched mode converter, although not for a few hundred pounds.
But, surely the sensible approach is a device that disconnects the supply in the event of the PME earth exceeeding 70V to local mass of earth, as detailed in 722.411.4.1 option (iii). Put in two small spikes nearby (resistance need not be very low, and the two would allow for automatic monitoring of resistance), see the green light come on and the job is done. It's basically an improved version of a VOELCB used for a more suitable purpose, obviously with a bit of engineering to make it reliable enough to switch the PE as well as the live conductors.
I have to wonder why the charging point makers don't offer an integral solution. 722.411.4.1 option (iii) even suggests the voltage detection device could be included in the charging equipment. The convenience of being able to install one product to any supply without further complications would surely be attractive in spite of increased cost.