I think the question on many people's minds is gonna be, "where is Varian Wrynn, the Lion of Stormwind?" Not an Alliance main, but his absence is notable.
Disenchanted, nothing was left to go to SL
I think they keep some major characters for later patches, or we might simply not see them, the realms of the shadowlands are many, if not infinite, we only got to see 4 of them at the moment so not every character from Azeroth will end up in one of those.
Supposing Varian's soul wasnt disenchanted by Gul'dan I imagine Varian would definitely go somewhere in Maldraxxus, supposing there isnt one of the other infinite afterlives he would be better suited.Feel like we would have found him if he was supposed to be in a place we visit though, especially if he went to Maldraxxus, that is a place that greatly rewards those with the most resolute spirit, and Varian sounds like he would be a shoe-in for the House of the Chosen.
Another thing we have to think about is future content - there are currently 3 open conduits in the Shadowlands, so it's possible we call down additional gateways and go to additional realms later in the expansion. We have no idea what the raid tiers even are, so it's either a raid pops up in all 3 other zones or it's possible we get more realms to explore. Big vision, doubt Blizz would see it through.
I sort of suspect Varian's soul got incinerated with his body by Fel energy when Gul'dan fried him...
I love these little Easter eggs! I stumbled upon another one in Revendreth and I'm not sure if wowhead made a post yet but Dr. Krastinov's sinstone is in the Halls of Atonement open area!