Is there a cut down certification category to cover only exhibition fly pasts?
I think the experimental category could be used for that.
I suspect, if they're serious, they'll have something like the Breitling Super Constellation in mind. If a sufficiently deep-pocketed sponsor can be found, the project is feasible, IMHO.
I wonder if our resident Concorde People would be willing (and allowed) to help out, e.g. training pilots, consulting, ...