One of the biggest problems with Azir is his manacosts
A part of why Azir is such a beast lategame is that his manacosts do not grow on rank, they stay the same, unlike a lot of other champions. This makes him able to get a full build without even needing a mana or manaregen component, so he can go for even more of a crazy scaling build.
Giving him scaling manacosts could help limit that and force him to take
or some other mana item that has less synergy (since CDR doesn't give him attackspeed anymore, for instance).
Of course he's still very complicated to balance due to his incredible power status in competitive yet very low winrate otherwise.