Well I think they are waiting to see if people want to buy such a big kit. They are making bigger and bigger as you can see with the release of the F-105. I think they are also testing to see how much people will pay for a monster kit like this. But trumpeter has a 100% record so far on releases, no cancelations. Unlike Panda and the myhical 1/32 B17 and P-47.
P.s. the F-105 took 3 years to be released so I hope it wont be long now.