There will never be another SST, not in our lifetime. This has probably been mentioned here before, maybe even by me, but when it takes 90 minutes to get from the west end of London to checkin, saving an hour or two on the flight times is not worth the extra cost. The average speed of traffic in London is slower than horse-and-cart Victorian times - it's 6 mph. Plus there are huge parts of the planet (the bits with people on) which are a no-go area for anything that generates a sonic boom. Planes piddle along at subsonic speed not because of restrictive gov'ts or whatever, but because the market for a profitable line of aircraft doesn't exist. There are few routes suitable and few passengers willing to pay the $$$ to save an hour or two. I wouldn't pay - is 5hrs45 en route NYC-LON so horrible that it's worth paying not £250 in economy on a 747 but maybe £1000 on a NG SST to fly the same distance in 3 hours? No, especially when you're not halving your journey time, but maybe cutting it by 15% (counting 90 minutes each end for ground transportation, 60 minutes check-in and 60 minutes baggage reclaim and customs / immigration) - journey times are 747: 10hrs45, SST 8hrs.
A SST biz jet would make slighly more sense.