Exactly this! Who needs them to tell us any concrete info when we can have much more fun picking apart and analyzing badly pixellated tooltips and half-seen text from low res videos? I would much rather see a dozen new screenshots for us to coo over than for them to come out and outright tell us the remaining civs, wonders etc.
Seriously, I expect we won't see much in terms of gameplay changes. They'll probably just be repeating what we heard in the recent press releases. I dare say they'll confirm 1-2 more civs, probably Assyria as they're all-but confirmed anyway and maybe choose to announce one more civ they know will stir things up a bit. They'd certainly get a BIG reaction if they confirmed the Zulu, although given the fan demand for them, they'd probably also get a big reaction from confirming Indonesia or Kongo too.