"A good replacement for Concorde"?
Hmmm, one flies at Mach 2 and cuts Transatlantic journey times in half. The other flies at Mach 0.95 and does the Atlantic as quickly as a Convair 990 or a VC10.
This is hardly innovative, is it?
To make a worthwhile reduction in journey time you need to save the pax 50% - say 4 hours across the pond, which would infer Mach 1.3 or so.