Boeing claims there is "considerable" interest, whatever that means. Marketing departments talk a lot of bullshit. They have to.
The only major airline that has openly expressed to be interested in the 747 Advanced is CX
But I assume that JAL and ANA could be interested as they seem to be reluctant to order A380s, but still need something bigger than 773s to start replacing their early 744s by 2010.
Qantas, NWA, SIA are possible customers as well. Once SIA has phased out the 744 and got A380s they will find the gap between 773s and A380s is to big to be ignored.
Here in Europe BA
are at least not opposed to a new 747.
If you look at the major 744 operators which are not keen to order A380s you will see that there is a potential of more than 100 744s which need replacements between 2009 (likely 747 Adv. entry-date into service) and 2015.
and JAL alone have ca. 50 744s which will be 20 years old during this period.
No airline is under pressure to replace their relatively new 744s though. And this won´t change in the next 3-4 years. I see that as a major reason why progress on this project is very slow.
Compared to that airlines have far more issues in the 7E7/A332 class where Hundreds of 767s and A310s need to be replaced pretty soon.