As far as I know almost all AH skins will remain in 1024 by 1024 res for the foreseeable future. The exception is very large aircraft, probably just four engined bombers. Currently the only one of these that is 2048 res is the B-29, however if and when the Lancaster, B-17 and B-24 are updated or any new one introduced I would expect them to be 2048 res skins as well.
It is mainly down to surface resolution, i.e. what area of the real object is represented by a single pixel. On something like a B-29 a single pixel could cover three or more times the scale area as on say an I-16 if they were built to the same res.