While it is no longer there, the Legion pre-patch was temporarily up on the background downloader. What could this indicate?
(EDIT: It's back up! Still doesn't mean it's coming next week or anything.)
Well, Legion is now less than two months away, and so we're getting pretty close to the point where its pre-patch (7.0.3) should be coming out soon. There's a whole launch event this time, and some really huge class changes. The launch event is also going to include things that we've typically never gotten before the expansion itself launches - Demon Hunters will be playable for those who have already pre-purchased the expansion (it's not clear whether they'll be available immediately or if there will be some kind of unlocking later on, but I'm hoping for the former,) and we'll also get a big event scenario that actually takes place within the Broken Isles (this is a limited, instanced thing, so don't expect to go traipsing around Highmountain just yet.)
So how long will we go between 7.0 and Legion's actual launch? Let's look at the historical record!
October 14th - November 13th
Warlords' pre-patch lasted almost exactly a month before the expansion came out, which I think is more or less typical.
Mists of Pandaria:
August 28th - September 25th
Again, almost exactly a month. Mists had the smallest pre-expansion event of any expansion, consisting solely of a single scenario, the Fall of Theramore, to be played at level 85.
September 7th -October 12th - November 23rd - December 7th
This one is complicated by the fact that Cataclysm had three major patches pre-launch. The first involved essentially no real changes to the game itself, but had events for the Alliance and Horde to reclaim Gnomeregan and the Echo Isles (respectively,) justifying the eventual new starting locaitons for Troll and Gnome characters. The second was the systems change - its alterations of talent trees and such, which also included the Elemental Unrest launch event in which players infiltrated Twilight's Hammer and fought elementals coming out of various rifts throughout Azeroth, culminating in special 5-player boss fights with ICC-quality gear drops - and then the Shattering itself, which unlocked new race-class combinations and brought about the changes the the Old World with its new quests and ability to fly.
So, not counting the Echoe Isles and Gnomeregan events, this was nearly two months of pre-patch, with two weeks allowing for players to try the new quests.
October 14th - November 13th
Once again, almost exactly a month.
December 5th to January 16th
The first expansion got about an extra week of pre-patch, but once again we have about a month.
So, with that history in mind, let's think about 7.0.
The only case in which there has been significantly more than a month of pre-patch was Cataclysm, though this was due largely to the massive transformation of the old world. In a sense, the post-shattering patch was sort of the true launch of the expansion, while its "launch" was the unlocking of new zones and races. Cataclysm also had the most complex and ambitious launch event of any expansion to date, so giving that a little more time may have been the wise choice.
Legion is certainly a return to form in terms of launch events (though I don't know if there are quests that simply haven't been unlocked on the PTR - being unable to complete the Broken Shore scenario is a big limitation) but I still don't think it will quite match Cataclysm's massive overhaul.
So let's assume that it's four weeks of pre-patch, like most expansions have gotten. That puts 7.0's release on August 2nd. There's wiggle-room there, to be sure. An extra week of pre-patch would put it at July 26th. Two weeks would be July 19th. But I think that they're highly unlikely to launch earlier than that, as they want to keep the momentum of enthusiasm rolling for the expansion itself.
So, my proverbial money is on August 2nd. Which is too bad, as I'm out of town then.