I've seen this done a few times. It's a fun game-mode IMO. The map has to be built around the idea though. Turbine, 2fort, etc. wouldn't work too well with it I think.
Here's an old classic you might want to take a look at:
The Powerhouse!!!
http://s90652007.onlinehome.us/ctf_powerhouse.html
Download link is on this page:
http://s90652007.onlinehome.us/
The map is one of my all-time favorites. I seldom see it played anymore, though

. There are two main objectives:
1) Capture and control the Powerhouse (a single control point in the center of the map)
- Controlling the powerhouse activates a protective shield around your Intel
2) Go for the Intel
- When the powerhouse is held by your team, the opposing team's shield will be deactivated...allowing you to take their intelligence
I know that your idea is slightly different with three points, but the concept is more or less the same.