Every year I like to do Blizzcon predictions. This'll be the 3rd time I've done it. The first couple times I did okay at my predictions, not being totally on the ball, but generally not being totally off either (though, frankly, I don't think anyone predicted Overwatch).
With Blizzard announcing they're no longer announcing subscribers for WoW; Activision buying King--the makers of Candy Crush; the Overwatch Beta already launching; StarCraft II's "final" expansion, Legacy of the Void, with a release date of just after Blizzcon; and Legion already getting the big announcement at Gamescom (which was my secondary guess, after last Blizzcon); Heroes of the Storm released in June and has been getting incremental updates; and Hearthstone just had The Grand Tournament released; it all leaves not a whole lot exciting to be announced.
So with that in mind, here are some of my "predictions". Take with a large grain of salt.
World of Warcraft
Let's start with the 500lb Gorilla in the room (who isn't already in Overwatch): WoW. We know Legion is coming, we know we were told we'd get a Beta before the end of the year.
I think we'll get a Beta date announced, and I believe it'll be just before Thanksgiving. We still have the 6.2.3 PTR up, so I doubt we'll see both that and a beta running side-by-side, so we'll probably see 6.2.3 finish up, then the Beta PTR go up late November.
We'll probably get a few more details on Class Halls, maybe some of the dungeons they didn't flesh out at Gamescom, and artifact weapons. Maybe some more on PvP talents as well. Mostly just refinements and smaller details of what was already announced at Gamescom. Otherwise, I don't see too much more coming on this at this time other than the beta itself.
Maybe, maybe, we'll see a general expectation for the release (Summer or Spring of 2016?). That's a pretty big stretch though, Blizz rarely likes to lock down releases that far in advance.
Honestly, probably very little. The schedule says they'll talk about the future of SCII after Legacy of the Void, so expect some eSports stuff, and perhaps Blizzard will announce or talk about some sort of Battle.Net infrastructure extension for holding tournaments and the like. New ladder formats perhaps. But in the way of content, I don't forsee much new. They'll be focused on the launch itself (November 10th!).
Also probably not much new here. They literally just went into invite-only Beta, so perhaps we'll see some talk about what went well so far and what hasn't, and perhaps some of their near-term plans for what the beta will see next (game modes or maps, perhaps). But otherwise I expect this to be relatively low-key aside from hype hype hype.
The schedule has a single panel for DIII, which really says that either they have an expansion in the works and they're not ready to talk about it, or more likely, that DIII is now in maintenance mode--given the previous 2 Diablos only had a single expansion each. The panel will talk about new zones, sets, legendaries, features, etc. but for the most part I expect slight expansions on how Seasons work (since they're working pretty well so far), and generally small upgrades to the experience over time.
Heroes of the Storm
Schedule says we'll hear about new maps and new heroes, so I guess that's what we'll hear about. The one interesting thing with games like Overwatch and Heroes is that they're very good for releasing fast incremental content, but big shebangs like Blizzcon I don't think you end up with much meaty to chat about.
Last adventure module was released back in April, so I'd expect a new adventure module incoming. Maybe Ulduar? They haven't really done anything with an Old God dungeon yet. They've done Naxxramus (undead), Blackrock Mountain (dragons/dark dwarves), Gnomes vs. Goblins, and The Grand Tournament. Or perhaps they'll go with something Demonic themed to go with Legion. Mount Hyjal?
I also expect they'll start talking about card deprecation. Hearthstone has a problem where ever-expanding card pool is creating problems for folks coming back, power creep, and for developer balance. Magic The Gathering handles this by deprecating old cards, but keeping a central set of "common" cards. I don't know how Hearthstone will handle it specifically, but I imagine we'll see some sort of deprecation mechanic (or cutting edge vs. legacy card mode). This one is a bit of a bigger stretch, but it is becoming a problem they need to solve, and soon.
There's no crazy gaps in the theater schedules, and I doubt Blizzard has yet another new IP ready for show (though they may be working on something). I imagine Battle.Net improvements will get rolled in under StarCraft II (which has a number of panels).
Overall, my predictions are pretty conservative this time around, but that's because Blizzard has started dropping expansion info and bombshells willy-nilly rather than only at Blizzcon. They've been much better at keeping information flowing all year round, so Blizzcon this time will probably feel more like a celebration of existing work rather than an announcement platform.