A unique (?) champion concept.. lol
Dunno how unique this concept is but...
A champ that converts all AP to AD and all AD to AP with certain ratio adjustments
So if you want full AD, you gotta build AP items vice versa
Certain item passive (like armor/magic pen) are tweaked so that they can be consistent with your scaling (who would wants armor pen when the 40 ad from last whisper is being changed to AP?)
His ultimate is probably gonna determine which stat (ap or ad) is the highest via a ratio formula and then get the real stats of the items he has for a short period of time
So if he has a doran ring, the 15 ap will be converted to 8 ad (idk) but upon activating the ult he will receive the exact stats of the doran ring (15 ap) instead
All of his abilities have both scaling cause it will make everything more fun
Oh, and the atkspd and crit stats from ad items are converted into AP unless he ults himself
I dunno I'm bored
for example. The combination of flat AD and Armor would ultimately change the value of that item, not to mention any active and passive effects. It sounded like you were recommending a conversion of those other stats into their opposite equal as well. At that point, you might as well just skip this whole idea and make the champion scale on existing items because the conversion equations would be a balancing nightmare.