So currently Coven weapons are acting as this White Whale for people to obtain the "best" weapon possible in the game since they are 5 IL higher than all the other gear.

What about, for 4.0, rather than offer a completely different weapon for players to obtain you challenge players to 1 last quest, which will take some time, but if they complete said quest with the requirements(which would never be nerfed), they would be given a final upgrade to their relic, which would be nothing more than vanity.

Basically one last grind that also uses Extreme content to encourage these relic users to do content they may have avoided. Getting to the max IL with these can remain casual, but why not have the last challenge, one of pure vanity be about a player actually using their weapon for the content they may have never tried otherwise?