It doesn't, strictly speaking, address any mechanical issue that comes up. It removes the issue that shows up at the table, namely one person having too long in the spotlight, and it ameliorates the issue of straight nuking someone with no recourse on their part.
Those are the problems that really stress my games because they make it really un-fun.
I'll ramble a bit here on mechanics. It helps me think. From a mechanical perspective, the problem I see is action supremacy. It should be possible to build characters of all stripes that are on a relatively even power curve. I like stacking penalties for this (ie -1 per action). If you apply that -1/extra action to all rolls (including defense), it gets some more teeth. Maneuvers complicate things a bit. Maybe the penalty starts at -2, and increases by -1 per extra action beyond that (-0 for 1 action, -2 for 2 actions, -3 for three actions). With a stacking penalty, I'm not overly worried about much beyond the low-end of this scale. Larger penalties to every roll make it very unappealing to go higher. So, take a -2 penalty to get 2 aspects on a scene. If your character tags those, then they only net +2, same as with a single action. So it's mostly useful for support play, which is cool on my watch.
So, a system I would like to playtest is this...
A stunt for each additional action of a given type. Want to attack 3 times a round? Requires 2 stunts. Want the option make either 2 attacks or 2 maneuvers? Requires 2 stunts.
First additional action in a round garners a -2 penalty to all of your rolls (actions, skills, defense, etc) until your turn in the next exchange. The penalty increases in severity by 1 for every additional action you take. I would be willing to consider stunts to reduce the penalty for certain, non-action, rolls such as defense. You also have to declare any supplemental action at the start and that -1 will affect all actions on your turn as well.
So, with this system, you can build a flurry type character who focuses on being very active on his turn at the expense of efficacy outside it, or you can build a more deliberate character who instead focuses on a single, high-potential action. I feel like this would be pretty evenly balanced, certainly more balanced than claws + breath weapon vs evocation. But I could be totally off my rocker and this is worthless. Like I said, new to the game.
Thoughts? Questions? Rotten produce to throw?