(disclaimer obviously: wild speculation for entertainment purposes only)
First - we don't know if this is legit. The source is in doubt. Unlike the Bolvar Lich King high-res which appears to be from a cinematic.
Second - the alleged leaflet logo and art look really, really good. If fake, I think it would have to be a deliberate mislead from Blizz, and I don't think that's likely. A lot of work appears to have gone into both. Like, a lot a lot. Quite a few professional hours.
For the purpose of this thread, let us assume it may be real. What implications could there be?
-Bastion appears to be an almost Greco-Middle Eastern inspired as well as an Elven city. (Suramar meets Elysium)
-It looks reminiscent of Elune. Elune is sometimes said to be a sheperd of the dead. An upstart goddess? Do the celestial Kyrians serve her? Could we meet Elune? A Kyrian allied race for the alliance? And a secondary Bastion-based race for the Horde?
-Bastion would be a perfect place from a neutral city and our adventures to start. And a city under siege, like we've gone to the rescue of so many times (callback to that feeling when you land on the beaches in TBC, WOTLK, Legion etc.)
-Themes and names seem related to D&D. Which has served as frequent (main?) inspiration for the Warcraft and Warhammer universes (all stemming from LOTR and norse folklore etc.).
-Bolvar or the amalgamation of Nerzhul, Arthas and Bolvar that exists now, may raise Death Knights from the soldiers fallen in the fourth war, to aid the Horde and Alliance in bolstering their numbers. Arthas said he did not fully unleash the scourge and that there was a reason for that. Maybe that reason is still balance. Maybe Bolvar also must help maintain that balance.
-Sylvanas may be working with other dead and undead powers, or even Old Gods, in the Shadowlands to take over Bastion, and perhaps defeat Elune, taking full control of a realm of death and undeath
I can't wait to find out this weekend. I haven't been this hyped about WoW since WOTLK. I think the potential for story telling and content here is absolutely amazing