the 380 is a niche product.
The market is not big enough for 2 types.
Boeing will though jump in and fill the gaps Airbus leaves open.
The Concorde, SST, 380, ... all niche products.
The 380 sells fine, but it is open, how the future will be, it might be possible, that Airbus has reached close to max sales of the 380, or at least major sales figures are already down. Maybe I am wrong... We will see...
That is what Boeing will do.
Airbus has, IMO, major orders down for the 380, a number still to go, but major down, so why should Boeing waste years and Billions to come up with a plane that enters service in maybe 2012-2014 to compete with the 380? Does not make sense in a niche market.
They already have several 777 to match the 340 quite well and the 744 on top, including freighters (744F and 772LRF...) and there is still a gap which might be exactly a niche as the 380, or a big market, but it is very likely there is a market for something in between 380 and 744.
Also, Boeing will have to focus on a 737-thing, the 320 is quite old by now (which means, it can be easily targeted by a new product). So the 787 brings technology for the future. The 350 is just a match. If Boeing focusses on developing future technology and not just meeting today's demands, they will have some nice days coming up, some bottles of Moet will be opened here in the West Loop...