I think you're going to be waiting a long time for any Mac updates. IPACS has said nothing for months.
It looks very much like they have abandoned the Mac platform.
FS2 on the App store stopped getting any updates 2 years ago even though the Steam version was still updated - at least they offered people a free changeover from the App store to Steam.
A Mac version of RC8 was never even offered on Steam which is very surprising - if they already have an App store version surely it would not be hard to publish if via Steam as well. The same goes for RC9 - if IPACS were serious about supporting the Mac why not make this available via Steam and offer RC8 App store users a way to move to Steam like what was done with FS2.