An overhaul to fix the problems with mage classes
Problems: 1: All types of mages rely on the same item group. This leads to items not feeling unique for each mage subclass, and splash damage when one items are abused with one class and end up nerfed for everyone. 2: All mages (well, almost... Ryze says hi) rely on a single AP scaling type: Total AP. This leads to only going with the best of AP items, and leads to balance issues and fairly stale builds.
Proposed solutions: 1: Give all champions a Base Ability Power, and an Ability Power Growth stat. 2: Adjust all champions with AP ratios to use either Base AP, Bonus AP, or Total AP. 3: Adjust items Ability Power stats, and adjust some of the scaling items (Ludens, Hextech actives, Nashor's Tooth) to utilize Base/Bonus/Total AP scalings. 4: New items to fill in gaps in items geared towards certain subclasses.
The fallout: 1: Mage subclasses would have differing strengths. 1a: Battle Mages would have a good Base AP and AP Growth, with lower AP scalings on abilities and above-average base damages. 1b: Burst Mages would have lower AP/Growth, but higher Bonus AP scalings on abilities and average base damages. 1c: Poke Mages would have Average AP/Growth, high Total AP scalings, and lower base damages. 1d: Enchantresses/Healers would have Lower AP/Growth, with low AP scalings and average base damages on damage spells, with closer to average on supportive/healing spells. 2: Ability Power items would all have their AP stats retuned. Items could be better tuned towards their target subclasses. 2a: Some items would have AP scalings added/adjusted. Hextech actives, Luden's Echo, Nashor's Tooth, etc. 2b: Base Ability Power Sheen upgrade could be made. Yes, it will probably be used on AP Ezreal. 3: Better potential for hybrid champion to be balanced around both damage stats. 4: Additional balance levers for new and old champions alike, hurray!
It would be a significant change, but wouldn't have nearly as big an impact as it looks. You don't need to relearn champs as heavily like during a class update. It would take some time to adjust for sure. Item and rune builds would change a good bit for many champions. Laning as/against champions would also change a bit, as players would need to relearn their damage outputs at item/level thresholds.
Thoughts/Idas/criticism welcome.