@Riot:A Spell Copying Champ

I have been playing Dota for bit and recently fell in love with Rubick,the Grand Magus.Why ? Because he has the ability to steal spells from the enemy team that's why. It's just a blast to watch your enemies run from their own powers and it's an experience I enjoy.

This brings me to my question. Would a champion with the ability to copy the spells of enemy champions be to hard to balance ? Is my idea of mimicry hero just a fever dream ? I imagine this falls into your whole 'burden of knowledge' thing where I suppose it would to hard for the average player to remember all the spells at his disposal in a given game.