Of course, Musk's comments are usually the only source for what may be coming next. And since many of his past predictions of what new features will be released - and when - haven't been very accurate, it's difficult to tell exactly what will be in version 9.
It's likely Tesla has been running two source trees for S/X and 3, with some common code. Version 9 could bring those together so S/3/X software would be shared, having all 3 families updated at the same time, from common code.
There's a huge backlog of promised - and not yet delivered features - and while we'd like to see many of those included in version 9, would recommend taking the strategy of expecting less and being surprised to see more...