Then again, as far as we know Blizzard has never teased us about a release date. So if you want to start making your wild guesses now, that piece of information is a good place to start. If it's not WotLK-related, our second guess would be an announcement that Diablo 3 is being "thawed out" for everyone in the near future. Yeah, we know it's a (lame) stretch -- but that's half the fun of it!
Update: After some poking around, we've discovered something interesting. Out of all the Blizzard websites, diablo.com is the only one that points our browsers to this splash page. Simple coincidence or subtle hint? We'll let you guys be the judge.
Update 2: Apparently diablo.com has pointed to blizzard.com for a while now. It looks like simple coincidence is much more likely in this scenario.