Ah, These are out in the US - saw one at my local film supplier a few weeks back. Mentioned this in brief in a thread in July....
The Fuji back is different from the Polaroid 4x5 backs unfortunately. To use the film one must buy the back..... Here they're going for 220 USD.
The only film I've seen thus far is 100b45 but that may be what my supplier has ordered. I would expect they would release a 100c45 as well as the fuji 3000 in 4x5.