Make Sion two champions
So to preserve both of Sion's play-styles, Sion should be re-created into two different champs. AP: In Sion's lore, it says "Noxian necromancers reanimated the behemoth" after his decapitation. So, this would be where Sion gets all that AP power from. In this version of Sion he would keep his name "Sion", but I think his spells/Ulti should be re-worked to better fit a brawling AP type like Gragas. For this version I would stick closer to the original, making his passive something like a Banshee's veil passive where spell damage from champions is reduced by X number until a damage cap is reached, where it resets and he has to wait some to gain it's benefits. Q could stay medium-ranged stun, but make it a skillshot that passes through minions. W could be something along the lines of a Volibear roar, where it damages all those around him and slows them. Also, (I know, Im stealing from champions, sorry!) he could gain a shield based on how many champions it hits like J4's W. As for E, have it act as a mini Nashor's Tooth when Activated with a passive of addig to his maximum mana pool instead of HP. For his Ulti, I think it should be what his W is right now- a massive shield that explodes in an AoE after a few seconds OR when the shield is destroyed seeing as how it is his ulti and the damage from it shouldnt be negated (IMO)
AD: Ill refer to AD Sion as Chopper, seeing as that's his Ax's name. Chopper could have his E passive made into his normal passive, his Q a dash (He is "a human battering ram"), an AoE insta damage spell to fit with his old W, and his E an average steroid with a bleed passive or something, keeping his Ulti. Thanks to those who read, would appreciate feedback! @Riot, if you read this ILY even if you laugh at it :)