I don't think riot would release a champ that can only be played only by duos. If they release him as I suspect they would you'd get even fewer support players because no one wants to be forced to play Chogall or they get a troll player on him and their KDA tanks as a response to something they literally had no control of.
He'd also be unplayable in ARAM and who knows what would happen in 3s.
Warding would be a nightmare with such a champ because the guy with the support item is stuck doing what the ADC wants.
IDK how they'd balance his health pool and mana pool.
What happens if the other player disconnects or rage quits?
TBH, the person playing B*tch would need an overpowered and potentially kit to compensate for lack of agency and I don't think riot would let that happen.
Frankly, I think Kalista is the closest we'll ever get to this idea: a separate champ who mechanically gets a bonus being tethered to someone else.