Concorde was more-or-less viable for BA (though not for AF). Specialized maintenance for such a small fleet (because it effectively only operated the transatlantic route due to regulations) was the thing that killed it economically.
Concorde used to serve a lot more than just the NYC-London/Paris route. It used to serve Bahrain, Rio de Janeiro, Dakar, Caracas, Washington DC, Miami, and Mexico City. Those faded away due to a lack of demand. (Ignoring Dallas and Singapore, as those failed due to restrictions on supersonic flight.)
I'm sure a new design could be a lot more economical. Of course, regular airliners have become a lot more economical as well, so it's a tougher bar to clear.
Concorde was more-or-less viable for BA (though not for AF).
I'm genuinly interested.
Thank you very much.