Boom is the latest to jump into the SST fray with this Mach 2.2 beauty:
Boom is HQ's at Centennial Airport outside Denver. Their hope is that the advances in materials, aerodynamics and engine technologies achieved since Concord was designed (Early 1960's) will permit them to keep the aircraft's per seat operating costs low enough to turn a profit. The airframe is sized to accommodate 45 to 50 seats to keep the load factor high. On key business city pairs (JFK-LHR, LAX-NRT, etc.) there's probably enough demand for a few dozen aircraft. Add a few more for corporate, private and nation/state travel and they might be able to make a go of it.
As was noted several posts above, Richard Branson's Spaceship Company will be handling the construction and flight test of the XB-1, a smaller proof of concept vehicle which is expected to be fly late in 2017. More info is available at
www.boomsupersonic.com