I've actually tried something similar to this before. My layout was bad, but the gamemode design is also unintuitive to the players. As tyler said, capping the last point is messy because players will get confused about the win condition. "Hey we own all 3 control points? where is the win", and only after taking and subsequently losing the point will they understand the timer.
I also may not be fully understanding what you are trying to do. I'd be interested to see what the hud/layout would look like, and if the timer doesn't refresh or whatever you choose. However, I'd view this as cp with a twist. Might not necessarily be "dynamic" though.