OK, I just compiled a list of all the obelisk appearances in the 5e adventures I could find so far:
Princes of the Apocalypse (in the Temple of Black Earth)
Out of the Abyss (a shattered, but partially rebuilt, obelisk is in the Whorlstone Tunnels under Gracklstugh)
Storm King's Thunder (stolen by cloud giants from the town of Nightstone just before the adventure starts)
Tomb of Annihilation (outside the entrance to the Tomb of the Nine Gods)
Dungeon of the Mad Mage (In Shadowdusk Hold far down inside Undermountain)
Descent into Avernus (on Avernus, surrounded by seven smaller standing stones)
Rime of the Frostmaiden (in the fallen Netherese city of Ythryn)
Spelljammer (one of the random encounters in the Astral is a "Gargantuan floating crystal obelisk of unknown origin")
Phandelver and Below: The Shattered Obelisk (it's in the name!)
All these could be used as the 1 - 10 adventure that could then be continued into Vecna: Eve of Ruin, (other than DotMM where the obelisk is in a high-level area), presumably using the featured obelisk in some way to transition from the lower level adventure to the higher. And given that Spelljammer is featured on the covers of both the regular and alt editions, I'm guessing that that mysterious gargantuan obelisk is going to come into play. Oddly, despite Ravenloft featuring on the covers as well, I haven't found any references to an obelisk in either the adventure or campaign sourcebook.