Seriously? That's pretty nice! Although I could see some problems arising from that with alpha-weapons. So like, if you have a missile that drains 90% of the power when fired, but the power has time to go back up before it's done reloading, then the ship will never be able to fire (even if it should). I guess that the weapon could just be split into two systems though, so it's not that much of an issue.
And I think that you're right about turrets, those have never cared about their own capacity, as they can just draw from the main ship. It's worth testing out.