Yes it's been tried before but I haven't seen a tidy way of doing it yet and I am very close to a solution.
What I've got so far is a func_breakable that only takes bazooka damage (125ish) and it gets destroyed and fires outputs to dod_capture_areas. The map has advancing spawns, and off-site teleports which move the players around to their spawn area, this means I can put the capture_areas on the original spawns and not have them interfered with my other players. But the problem I am having at the moment is that when there are capture areas in other capture areas, only the outermost capture area works. So I figure if I have some complex logic and math entities that only let one of those capture areas enabled once at a time I'll be set. I've had a look at them but it's quite hard to figure out just how they work, and I've done little programing so... anyone have any ideas?