Maybe a little OT, but, when the U.S. Navy lost the gun tube in the USS Iowa incident, we in the military were told that the only way to get another was to take one off a museum ship since there was no way they could be manufactured today.
The Concorde will never come back, for all the reasons in the other threads. But, Boeing went as far as final 3D CAD drawings, mock-ups, and even initial tooling of some parts on the their "Tokyo Express" SST before realizing there wasn't (at the time) a market for it and the U.S. taxpayers (unlike the European taxpayers) weren't going to foot the bill. The problem of sonic boom remained unsolved. AFAIK, Boeing has the plans and could update them quickly (with more modern engines), but I haven't worked with Boeing for 6 - 7 years now. I suspect there will be SSTs in the future, but maybe the far future.