Another interesting thing regarding the A9: I was very surprised when I realized that it was made for the e-Mount, not for the A-mount. That means, implicitly, the A-Mount is dead.
Everyone said the A-mount is dead after the A7R came out, the A7R II came out, etc. Then the A99-II surfaced.
The FE mount gets the hot stuff first because the mirrorless market is popular for them, and because it allows Sony to court CaNikon shooters (who can adapt the lenses they already own).
But Sony can always jam most of that same technology into a future A-mount rig. For instance, the A99-II is effectively an SLT with the A7R II sensor.
The A-mount is certainly Sony's second
most important (stills camera) mount, but I think it will live on. It will just have slower refresh timing than the FE mount.