I'd like to see his abilities gain their mana scaling by level. Similar to Lucian's Q.
This would reduce him as an early game bully and a late game power house.
Another option could be to put some of this power into his ult. Currently his ult is not required for him to be at full power. It's mostly a surviability/mobility ability. While it does grant AoE and proc's his passive, I think it would be the best place to transfer some power to. Every time you see him, he is at least 90% power without his ult. Isn't that why Darius got his ult nerfed? Every time you go to lane he has everything he needs to beat you.
That and his E turned into a skill shot. If it hits a target it'll bounce, working like it does now. Perhaps add some mechanics to it so that it can bounce based on where it goes. Kind of like you were playing pool. But that may prove too difficult to program for all I know.
Another idea could be to rework his passive. Change it to grant bonus damage based on max mana for every repeated attack. Meaning just landing a Q wont be quite so powerful. He's gota combo the abilities. Using R could ignore this part of his passive.
I don't partially care either way, I don't play Ryze. But I'd be disappointed if they destroyed what made him who he is in a rework. His most iconic thing is his mana scaling.
In short. Less early game damage since he is a hypercarry. Some power shifted into his ult to make it more important. Some form of skill in his kit beyond using his passive to it's most effectiveness. And even then that can be widely determined by ping.