I absolutely love Kassadin, as he was my first main I ever had. I know that with him being pretty strong right now, some people don't like him, but just look at him. He looks pretty bad right now, but with his lore and theme he could totally look amazing.
The mini VU he got a couple of years back will probably be the best you'll have for the immediate future. They didn't do anything when Kai'sa launched, so I doubt there's any immediate intention to do anything with him.
I doubt that a VU would change too much about him, honestly, though I DO feel like they could stand to update the design of the Nether Blade, and give him some armor since his short story describes him as wearing it.
Bad? Not even. His visual update in 2015 made him look way better then he used.
http://2.bp.blogspot.com/-ZrRp-aZTa-Y/VOzs5V7nXdI/AAAAAAAABgQ/BgrNFRhebfk/s1600/kassbasecompare.jpg
If League of Legends is still a thing in 2025 that's when it will happen. He's super low priority
