I know some Xayah / Rakan mains will get angry, but they have a recall and ability they can use towards each other.
Some people have duos which aren't in the botlane, but have the same skin.
For example, Tango Fate and Tango Evelynn; a GREAT duo skin for mid and jungle premades. It's even dance based.
Of course, not like Riot would go and enhance older skins beside PF Ezreal.
But other skins, when encountering each other should get a duo dance.
The Dragon Trainer Duo, Tristana and Lulu. ( A dragon dance with Trist's Dragon )
Previous SG Legendary Duo, Ahri and Jinx.
The Witches, Janna, Nidalee, Tristana and Morgana.
The Slayer Duo, Jinx and Pantheon.