My guesses? The next major content patch:
- will be announced at BlizzCon in November;
- will drop late in 2013/early in 2014;
- will include the revamped skill and item systems,
- will finally allow them to balance the game properly, making proper PvP content possible.
The next patch after that might include the team deathmatch mode; it'll certainly be in the 1st expansion pack, along with more story, an additional class or two, and maybe additional PvP modes. Apparently, the Blizzard team have rediscovered their love of the modding community, so look for an offline play mode and mod tools sometime next year, as well.
In the meantime, in a bid to keep PC players engaged in spite of a lack of details or substance from the developers, the Blizzard team will finally engage in more community outreach, although mainly through fansite interviews and podcasts, rather than through the forums; perhaps the atmosphere here is just too toxic. Look for only discussions of generalities and game design philosophy, though, and no detailed info about the next patch or first expansion until late October at the earliest. Also, look for Blizzard to stop using phrases like "talking about" when discussing game features; apparently, they've also finally twigged to the fact that the community hates this phrase.
Speculations are my own, naturally, although unlikely to be unique to me.