Togekiss is a great supporter and almost perfect for duel too. Duel side has two problems: Tri Attack's Formula and Healing Wish.
The problem is new Tri Attack formula, if they bring the old one that had a chance to apply Sheer Cold's effect, idk if some of u guys remember that but was great in Porygon2 and Porygon-z for duels.
Also, I really don't know why they changed healing wish and kill Chimecho and others pokes that had a certain relevance in duels and sometimes appeared, now dueling is only based on pokemons of the moment. I don't think if they let healing wish heals itself how it supposed to before would be overpowered cuz its demand sometime to fully heal.
If u create thread for rebalance just present the reasons u didn't show to us. If u really want it for duels maybe theses change is enough, perhaps add natural gift to tm learnset cuz Togekiss doesn't have any counter attack.