Keep in mind though that BfA was faction war themed (and a bit of Death and Old Gods as well), but the rewards were mostly about Kul Tiras and Zandalar. The shiny selling-points and leveling experiences of the expansion.
SL, similarly, didn't focus its rewards around Death specifically, but rather on Oribos and the aesthetic you see around there.
Same with DF. Clear focus on the different flights that we met and quested alongside in the campaign. Sure the theme of the expansion was the same but still, the trend continued.
TWW was pitched as a war inside Azeroth with the nerubians as our main initial foes. But rewards focused on the Earthen. Not even the more complex and nuanced image of the Earthen that we've gotten post-launch. The poster boy version with gryphonriders and storms, which was a theme that lasted what... 5 minutes before changing into something else?
So IMO (and depending obviously on how they decide to spin Quel'thalas at Gamescom), the most likely scenario is that the Midnight rewards just aim straight for players' affection towards Quel'dorei.
Some different bundles I could see, depending on where they land:
- Wood Elf / Ranger themed. Sort of what Sylvanas, Alleria etc. were like back in WC2 and WC3. Maybe a neat transmog set, a unicorn or drahonhawk mount, and a couple of weapons. Bow? Swords?
- Light-themed. Basically Guardians of the Sunwell. If Metzen has his way, I could imagine an almost "The Avengers" type of stylistic approach to High Elves in Midnight. Badass and larger-than-life heroes defending the Sunwell against overwhelming odds, and looking awesome doing it. Maybe not all of them, but an elite squad perhaps.
- Basically a mishmash of a theme that represents all iconic versions of High Elves we've seen so far. For example, a bow from Sylvanas, a staff from WC3 priests or some type of dress from WC3 sorceresses, and a face tattoo from Alleria. Something for everyone.