I learned long ago to never be in the first wave when a World of Warcraft expansion launches. So no, as of this post I've not gotten into Legion just yet. I'm going to post this, eat dinner, and then go into it.
The reason is that there is always a bottleneck of some sort or another, which results in issues that don't abate until that surge in traffic does. Past expansions dealt with this by having multiple input paths so that player traffic doesn't bottleneck immediately, only to run into one later, and that did not always work due to some bug that got overlooked or ignored during Beta testing. (Warlords had a bug crop up with one doodad Horde players had to use to finish the introduction series by establishing their Garrison. Wrath of the Lich King had everyone work out of one city, causing horrid lag.)
When new races or classes got introduced, those also served to reduce traffic at first by providing an alternate way to get into the new content. (I did this a lot.) Those folks made new alts and waiting for a later time to take their main characters into the new content. Legion messed with that somewhat by allowing pre-orders early access to the new Demon Hunter class, and it follows Warlords policy of giving a free level boost to all who buy into it, but so far it hasn't resulted in making things worse.
The streamers I follow reported a smooth launch so far, but there are issues with some questing zones cropping up and we're being funneled into one city again, so I expect old issues therein to return shortly. In the meantime, I will not hurry to the new level cap; endgame content won't be accessable for a few weeks, so hurrying only to wait is dumb. And that's all the rambling I'll do about it now. Time to face the Legion.