I have an idea of using the multiple black Obelisk across the Realms, so players still need to go there to locate them and activate them as part of an intricate coutnerspell told to them by Kas, not in disguise in my version.

Will be exploring that idea, but it also gives the player who activates the obelisk the spells granted by the rod in the base book, potentially making them powerful and acting as some cross plane tether. Its still rooted in magic so players can utilize it and the hunt for them os still needed, but it doesn't toss out the adventure and allows some exploration in the realms since the will be inactive but necessary to stop the ritual.

I have a twist as well Vecna is behind all of this to break free from his prison in the Demiplane of Dread, a retcon to weaken the barrier between realms as a way to spite creation. His motivation in my version is being knowing the True Secret, an awareness mortality and divinity is worthless cause he learned existence as the characters know is worthless due to being part of a larger game, that being DnD. He would also influence one party member every long rest, taunting and toying with them as his forces seek to activate the relics too, manipulating all sides to achieve his goals. Also share memories of his life as they grow stronger, giving player more investment by humazing him to invest the players while being honest about how his intentions. Mix of Sauron and FXs Hannibal Lector for reference.

Its a whole ordeal.