restoration of NX611 seems to be held to the same UK standards as commercial pax aircraft by weight class
From a
maintenance standard, possible, and well done NX611 team. From a
design compliance standard, not so easy. As a person who issues STC approval for modified aircraft, I deal with the reality that older aircraft can be very difficult to bring up to today's design standards for passenger safety. Included in aircraft for which I am responsible, are two very well rebuilt [Basler] DC-3's which are operated commercially. With a lot of work, and modification, they generally meet FAR Part 25, with a few agreed allowances. But, the DC-3 originated as a passenger/cargo airplane, not a pure military role. The basics were in place in the design already.
I've been involved with the restoration of Lancaster FM104 (I loaded parts of it with my tractor, for its shipment to Victoria, and assisted the team in Victoria with restoration planning. I have also spent time in the cabin of the Canadian Warplane Heritage Lancaster. I could not make the Lancaster compliant for carrying any number of passengers, by today's design standards. Similarly, I was asked to plan and approve changes to a PBY Catalina to allow commercial passenger carriage. 'Not easy. By the time we worked through what would be required (emergency egress), it was agreed as impractical, and the project not continued.
If eager vintage military plane "experience" passengers can demonstrate unusual passenger skills in terms of difficult egress, risk, and understanding the limitations of the design, fair enough, let them fly. But to market rides to the public without extra briefing does not comply with the exceptions of Mr./Mrs. Public for the latest standards of safety.