My turn at the crystal ball. What do event pros absolutely need, and what would get their attention, with even C/N chasing this? Super sophisticated AF - they all said so in recent interviews. It's still much easier to move around small files and clients don't need huge files. That I believe will be the basis for the a9.
So my money (quite literally probably) will be on a high resolution a7r style model. The things some users want are niceties to many folks using one, but given depreciation might not be enough to swing many of them to a new body, if the now aging (!) sensor remains. A top end sensor with great performance will. D800/a7r - these cameras have a certain aura due simply to their resolving power. So the higher res sensor plus the a7II adjuncts is my bet. Many a7r owners will simply keep that one as a backup or second shooter, in that case.
This would leave room for Sony to beef up the pro release - dual slots, more rubberised stronger body, stronger accessories like grips, dedicated flashes and so on - to get pro C/N eyes on that one. It won't need to compete purely on small size/weight if it's good enough. This is the longer term project, the reason it is last to appear.
Many of the lenses seem to point that way - 70-200, 35/1.4, 90m, the video zoom. They know many a7/r/s users are committed to mid/high end legacy, and they need to fill out the light FE55 style and Loxia lenses over this year, but they are not pro choices - they are enthusiasts' choices.
A four tier system - video/low light a7s with its special zoom, a7 low cost system entry camera plus the 28mm/coverters, kit lens with more to come, a7r with FE55/35/Loxia, 'a9' with pro zooms and large primes (maybe more on/near release), all users can mix and match.