Well in any case, if we do in fact have the data, then all this should be a walk in the park.
I am not at home to verify in hammer, but it seems like you could have this work.
You get your caparea to send the onnumcappers info to a relay of some kind. That relay would tell the math_counter how many points to add per tick.
Let's say you were trying to make an elevator rise in proportion to the cap speed (lets say its purely for aesthteic reasons, not for gameplay). You would make the thing into a func_movelinear that moves at one unit intervals. The SetPosition is relayed by a math counter that keeps counting up until it reaches 100, or down until it reaches 0.
The math_counter is influenced by some relay that tells it how many units to add depending on how many cappers are in the cap area.
Let's say at 100% speed the elevator (and the capture) would be all the way up after 10 seconds. One capper means it caps at 50% speed or 20 seconds. Let's also say that your math_counter updates every .5 seconds.
That means that for one player capping, the counter should add 2.5 points every half second, which should add up to 100 after 20 seconds.
A 10 second timer with 2 people on it captures in 13 seconds, so you should add around 3.8 per half-second.
3 people captures in 10 seconds, add 5 per half second.
4 people should capture ~9 seconds, add 5.5 per half second.
I'll admit I am not a math major, so if someone with a larger brain wants to tell me where i can put my history degree/poli sci degree, please help me out.