I don't see how this could hurt, assuming it caps after a few stacks. I don't want to see super max magicka + cost reduction sorcs one shotting people, no matter how funny it would be.
Although @Derra I think your time would be more productively spent petitioning for Streak to not incur a cost stack if you damage an enemy player with it. That will encourage offensive play like you want without affecting Streak's defensive nerfs, and it'd be a more realistic change for ZOS to push through since it would require many fewer resources.
Streak either needs better mobility and magicka cost OR better damage.
Definitely not both, and this is a sorc speaking.
Last thing I want is for the potatoes to spam it all day