I don't think the new larger 747s will ever replace the 744. I think Boeing hasn't been to focused on selling the larger 747s at this time because they don't feel it is the right time. When it comes, we may see Boeing really put this plan into action, and launch the new planes.
I think the 747 future is uncertain. JAL is the only airline I can think of that aren't likely to buy the A380. United are very likely to, they love the Airbus narrowbodies and certainly need the capacity offered by the A380. Northwest are the same, huge AI narrowbody fleet and in need of big planes across the Pacific.
Lucky for Airbus, most airlines make fleet purchasing decisions based on economics, and there is no way a 747 is going to be as efficient as a design 30 years younger. It is impossible. Boeing can either show the entrepreneurial spirit that kept them on top in the 60s and 70s and build a new big plane, or rest on former glories and be completely trampled and left with the 777, a few 737NG orders to Delta and AA, and a sexy looking Sonic Cruiser which will only ever exist as a screensaver.
United has expressed no interest (at least in public) in buying the A380. Northwest just ordered 2 more 744s, and they are likely to order more for 742 replacement, and again, they've never expressed interest in the A380.
The 747 design is old.........and there's really no point to that statement. This great designn has proven itself so much, that you can't blame Boeing for trying to continue it! Like it or not, I'm with Boeing and the 747 program managers who say the 747 will be in production for many years to come.
Now you say, as the 747 program dies, and then Boeing is left with the 777, who's orders have almost reached total A330+A340 orders combined, and in a much lesser perioid of time! You sound as if the 777 would be nothing great to be left with. ANd the 737NG? Well, don't even get me started on that aircraft's orders, it's well up there. The 737NG is selling like hot cakes. Again, you act as if these two projects are nothing great, and the truth is, they've been beating up Airbus sales ever since they were launched buddy.
I agree, the Sonic Cruiser probably won't be nothing but a picture, but with newer 747s, even with how much you seem to dislike them, it may be different...