And with Boeing's trans-sonic on the shelf it looks like it will be a while indeed before something else comes along ...
I'm not an accountant but you need to have the aircraft marketed before it comes off the drawing board in order to be able to afford it, and if people won't line up to buy, because they figure not enough will ride, never mind all the other issues of the day, then where are you? The Concorde would not have flown at all had it not been for Government support and national pride.
Don't get me wrong, I'm just trying to be realistic, and I hope a replacement happens in my lifetime, but even Douglas sold the DC-3 before he bashed much tin. The good news is they are going to museums and not the scrap heap.
Bruce