A lifetime ago, I worked on a large project that was never completed because Google released Wave, which addressed the same problem. Wave did it in a less useful way, but my employer (understandably) didn't want to go toe-to-toe with Google and so abandoned it.

The main part I worked on was to be able to do exactly this (not for CAD files specifically, but including those). It was a very difficult, but rewarding, problem to solve.