Summoner Spell Idea for Discussion: Rewind

This will probably never be added, as I can already see you guys screaming "BROKENWTFGOKILLYOURSELF!", but I just wanted to bring up the idea as a point of discussion.

#Rewind Reset all of your basic ability cooldowns. 300 second cooldown. Starts game on cooldown.

You see something like this in Heroes of the Storm, and it's extremely powerful on certain heroes like Nova and Muradin, letting them refresh their ability chain. However, it doesn't refresh the cooldown of their ultimate abilities and requires being taken over some other very powerful options.

While I'm sure this could be rather game-breaking on some Champions (i.e. Rengar, Renekton, Alistar, etc.), humor the idea for a moment and imagine that it existed in the game. What sorts of things would you do to balance it out?

("Remove it" is not a valid answer)