If Winds of Magic is anything to go by, I see them mixing some advanced careers and one Chaos power across 3 more expansions. I'm currently thinking 3rd tier Priests next including associated careers like Vampire Hunter, Tomb Raider, and Templars, along with Nurgle due to strong adversarial relationship with Shallya. Slannesh would get mixed with higher level Noble and Merchant careers along with advanced Smugglers and other seedy types, leaving Khorne for the martial-oriented career set. This would have more careers than the others since Khorne doesn't use magic, so no spells. Here's where we'll see advanced versions of War Dancer, Iron Breaker, and Sword Master, along with Mercenary Captain, non-religious Knights, etc. That gets everything out there for up to 3rd tier, leaving them to do 4th tier Wizards, Priests, Slayers, and other vertical career paths at a later date. Not sure where I see Halflings fitting into the mix, although they said they would be coming at some point back before the core was released. Also interested to see if they keep up the tactic of making every other release an adventure. That let's them dribble out NPC and monsters over time as well rather than release a big Bestiary type supplement.

Just for fun, I'll join in on the speculation...

• Bestairy - I believe that this one has already been hinted at
• Priest's Supplement - This makes sense in light of the Winds of Magic release, and I would think that the Chaos power to add into the mix to counter all the priestly virtue would be Slaanesh.
• Martial Supplement - Advanced careers for the more militant (and possibly rogue-ish) careers, which would also add in Khorne.
• Advanced Careers - a supplement for advanced careers not covered elsewhere - and of course featuring Papa Nurgle

Of course, I'd like to see an actual meaty campaign as well (multiple release as opposed to a single box), but that's just wishful thinking!