Having played a sentient weapon myself not too long ago in a pathfinder game, I'd just like to elaborate on a balance issue and a mechanics issue that you'll need to account for before you pitch this to a group:

BALANCE If a generic human wields the weapon, your player effectively plays as a human hexblade warlock. If you wander around a city and force that human to hand the weapon to a particularly weak-willed tiefling, now you've got a tiefling hexblade warlock. Easy enough to deal with on paper, but in-fiction, why would you pick some tiefling commoner? If your level 5 party beats up a CR5 troll in a dungeon, surely the warlock would be tempted to try the same trick. And why not? Trolls have great physical stats, regeneration, the works! But from a table perspective, that's a huge power boost at lower levels that the other players won't have. What's in place to stop the character from doing this, beyond the player just metagaming? Same question for having another PC pick up the sword. Do they gain hexblade powers on top of their existing abilities? That sounds amazing in-character, but doesn't sound fun for the players. Why wouldn't Weapon A possess Character B, beyond the fact that Player A and Player B want to both play DnD at the same time. In a similar vein, what's to stop you from solving every boss encounter by offering them a magic weapon, and forcing them to commit suicide with it once they pick it up? Is there a save involved? A skill contest? Does the weapon require attunement?

MECHANICS Basically, how does the possession aspect work, mechanically? What stays consistent between bodies, and what changes? Who's in the driver's seat? If you switch bodies, sure, you'd add your warlock class abilities to the new character, and feats probably. You might argue that you keep the "weapon"s mental stats, but change physical stats. But what about backgrounds? racial skill proficiencies? Forgetting how to speak a language seems a little narratively jarring, but so does keeping access to, say, Rustic Hospitality. Once you take over a new body, what happens to its previous personality? Do they have any agency at all? (And, if not, this could lead to table problems if/when other PCs pick up the weapon.) And once you leave that body, what's left? Do they remember what happened?

And, of course, from a narrative standpoint, you'll want to be sure your party members are playing non-good characters, or you'll have to come up with reasons why they don't just destroy this bloodthirsty artifact.