An earlier news article suggested that there wouldn't be an IMAX release of TF3 because it was being filmed with 3D cameras (which are a smaller size/resolution). But now it looks like the movie will be converted to IMAX, which is pretty much how most movies are done for IMAX (and most of the first 2 TF movies were filmed with non-IMAX cameras).

And it looks like the IMAX version will be released at the same time as the regular and 3D versions.

(looks like another trip to Sydney is on the cards mid-year)