CAs along the same lines has been done before (Score 1)

The Brazilian FreeICP project issues free certificates for two years now -- both for test purposes and with Verified Identity through a collaborative score system. I didn't go through CACert's full process just yet, but at first glance it seems that FreeICPs' trust scoring system is far more sophisticated, even if user friendliness needs improvement. I was also under the impression that CACert's client cert generation stuff works only on IE. FreeICP.ORG's also works on Mozilla, Opera, etc.

http://ca.freeicp.org -- for the Web CA
http://www.freeicp.org -- for the (rather old) main project wiki
See also the paper they published at NIST's 2nd PKI Research Workshop.