I'm really happy they're delaying Firelands. When I read that 4.1 was on the PTR I had the exact same feeling as I did when ToC hit the live servers: "It's too soon, we're not finished in Ulduar yet!". We're still progressing in heroic content and are not even halfway through and seeing how difficult heroic 10's are; I was hoping for at least a few more months to get to see Sinestra, a hope that has been re-lit.
As for War of the Ancients: I'm betting a lot that it's coming with Firelands.
Pretty much every tier (except ToC) has had at least 10 bosses available and Firelands has been confirmed to have 7, which leaves us with at least 3 more which means another instance which makes a lot of sense since they've stated they want to split up content into multiple dungeons, a promise they fulfilled for the first tier in Cataclysm. Also the story of WotA just fits so well into the Cataclysm-lore now that Deathwing is the main antagonist (for you who don't know, WotA tells the story about how Neltharion became Deathwing).
Reading through the datamined quests for the supposed legendary staff, you're talking to Anachronos. Who was he again? That's right, the bronze dragon outside of Caverns of Time. Guess what? He's not there anymore. And WotA took place like 10 000 years ago in WoW-lore.
It's just too many coincidences not to happen