While we've had the Emerald Nightmare since right after the launch of the expansion and the Trial of Valor for a good while now, tomorrow sees the release of the main piece of Legion's first true raid tier.
Nighthold will have ten bosses, and will be divided into four LFR wings, with the first wing launching a week from tomorrow.
Gear drops from LFR will be in the 855-865 range, meaning that even if you've been running Mythic dungeons or Normal Emerald Nightmare, there will be a decent motivation to run Nighthold on any difficulty, and that's before we consider that we'll be getting tier sets.
Tier sets this time around will actually include cloaks, giving players more flexibility if they want to get their 4-piece bonus (pretty important given legendaries.)
Nighthold's release is not really a patch (technically speaking this is 7.0 content) so I don't think we'll be seeing very much in the way of world content to come with it, but we got most of that through 7.1 with the Suramar quests.
With Nighthold, the first act of Legion will be complete - kind of crazy to think that this will happen several months after launch. But while I wouldn't expect to see any major content released before 7.2, the good news is that 7.2 will probably be going on the PTR not long after the release of the raid.
7.2 of course will be opening up a quest campaign on the Broken Shore, giving us a new faction, new class campaigns (that will give us class mounts, as well as branching artifact challenges to unlock new skins,) as well as a new dungeon and the tier 20 raid, Tomb of Sargeras, not to mention new world content like legion invasions in the Broken Isles, the ability to unlock flight on the Broken Isles, and heroic (in other words, queueable) versions of The Arcway, Court of Stars, and Return to Karazhan.
We also know that 7.3 will be taking us to Argus, though we don't have any details beyond that.
Thankfully, in huge contrast with Warlords of Draenor, not only do we have a ton of content already, but we've got a ton on the way.