I think it was a knee-jerk publicity reaction to the go-ahead on the A380 (ie they grabbed something they were probably working on quietly anyway, and thrust that into the limelight), but the fact remains that you will need more powerful engines (and hence pay more for fuel), and smaller cross sectional area (fewer pax- you can't stretch it much beyong 80 metres -airport constraints), which means the few pax on board (100-150?) would have to stump up big ticket prices..
Nobody at the marketing dept of Boeing is confident that there is enough demand for the project.. (remember A380 mktg hit the same panic for a bit)..
If noone wants it, noone will pay for it.. end of project, technology isn't really a problem, paying for it is.
King Patience