Usagewise, the top three AH 1.x units that need upgrading to AH2 standards are:
1) Panzer IV H
2) Tiger I
3) Lancaster Mk III
I would think with the Wirb chassis that the pzr4 is high on the list of "easy updates," so I'd bet it's going to be in the next update (or, the "next update that releases updated vehicles").
Lancaster has a lot of use for its bomb load, but there are still a lot of folks flying B-26s, Ki67s, and a bunch of the older models. We know that bombers take more time because they are more involved. What's the most used fighter with a 1.0 3D model?
I'm placing my bet here: I'm going to say Panzer, A6M zeroes, and F4Fs (that's in order of "Good bet, good guess, and just plain wishing")