That is a pretty interesting idea for a game mode! The KOTH hud could work if it was modified a little, too.
In my opinion, once in the meltdown phase the timer should be at maybe 40 seconds with a 10 second cap time- once meltdown is over (team caps or back), the timer should be set back to 40 seconds. This makes it so not only do you need to capture the enemy's point, but you have to stop them from capping it back more valiantly. In your version it would be too easy to just cap, drain enemy time, flee, and repeat. Hopefully you get what I mean by that. Hard pushes are my favorite thing in tf2, so it would be cool to see that!