As far as I know, there is currently:
1.) a TortoiseSVN based plugin for Windows only (obviously) in the C::B forum
2.) a cross-platform approach done by Thomas ages ago:
http://developer.berlios.de/projects/cb-svn/The second one is rather old and AFAIK no longer seriously developed. But you should better ask Thomas about that (PM him). However - you can have a look into that project to gather a few ideas (maybe...)
Other development in that direction is not known to me.
BTW: Take in mind that C::B is already partially designed for version control systems (e.g. file images, file type enumerations etc.) which you might want to use/enhance.
To sum up: Go ahead! If you like then try to think really generic in terms of control systems, thus have a look at CVS when it comes to important interfaces... that would be my wish... ;-)
With regards, Morten.