Overhauling AP into a spell amp system would be beneficial to the game.

Remove most direct ratios from abilities. Utility Ratios, HP ratios, and AD ratios on basic-attack enhancers can remain.

Cause AP to increase your ability damage by X% per point, and then rebalance the amount of AP you can get from items.

Give different champions different X values, to prevent Mundo from stacking deathcaps to get 100% current HP damage on his cleavers.

Suddenly, build variety explodes since suddenly, you aren't pigeonholed into having to build only half the game's items.

Some items would have to be reworked, like penetration and healing reduction.