This is helpful to know. I didn't realize the SDK for XP12 wasn't available yet. I would have thought it was available during the alpha so that devs could use the beta to beta-test their planes, so that upon XP12's release there would be finished and mostly-bug-free 3rd party planes to choose from.
I can be patient (sort of! ), but it would be a shame if they release the fancy new game and one of XP's greatest assets over MSFS (its wide variety of quality 3rd party aircraft) wasn't available at the time a lot of prospective buyers are hearing about the game.