The graphics upgrades that various old AH1-era planes have received recently have nothing to do with their flight models. In this era of VR the old AH1 cockpits look pretty hopeless which I'd guess is why HTC are so keen to replace them first. It is likely that the rest of the AH1 era stuff will be upgraded over the next 6 months or so, which means the Ar234, A-20G, Boston, Ju-88A-4, Ki-67, Me 163 and Tempest.
Unless some new flight data comes to light about a particular plane then it is likely that any AH flight model changes would be global, i.e. a revised post-stall or flap lift model. Such a revision might help some planes more than others but it would be unlikely to upset the MA status quo too much. While much of the plane set is not used much in the MA, AH isn't only about that arena and many of these other rides are needed for scenarios.
If HTC were to follow certain other "flight sims" and revise flight models on the basis of play-levelling, national bias or player pressure rather than by historical accuracy then they would lose a lot of their established player base.
