Boeing have a number of options here. If they really go to town, they could do a new wing, FBW, 777-style flightdeck, 787 engines, and maybe even 787 type systems. What they can't really do is significant composite structures, but they can use some composite in specific areas to save weight.
However, all the Boeing comments so far seem to suggest a simple stretch, new engines, and a modified wing. I think the 777 flightdeck is a given though.
I think the more Boeing offer, the larger the market will turn out to be...but I also suspect that they'll play cautious. Remember the more they put on the plane, the more expensive development becomes, and the higher (and riskier) the break even point.
But I would love to see them go the whole hog...I think there is a market for the 747+, that doesn't require the size of the A380. If Boeing build the right 747, I think they could take as many, if not more, sales than the A380.