AH2 will be a huge overhaul of AH. That is about the limit of what we know. The current AH plane models may or may not be compatible with HTC's new and improved system--they really haven't commented on whether that is the case, so we don't know. I mean, it wouldn't be taking HTC the better part of a year for this update if it wasn't a massive change.
Oh I'd agree that HTC will probably transfer over most of the current AH planeset to AH2. However, I wouldn't be surprised if some of the truly useless planes remain absent (un-used junk like the Hurricane 2D comes to mind). Given their timetable, it wouldn't make much sense to transfer over units which have proven to be worthless, unless the transfer is quite easy.
To counter that, I seem to recall HTC remarking that their new plane-adding tools are less time-consuming than what they currently have, which would suggest they'll be able to add new equipment at a faster rate after the initial release.
One unchanging fact is we apparently won't be seeing anything new through the summer.
J_A_B