What new features do you need that you can’t plugin yourself through the theme system?
“Forum was badly coded anyway found loads of vulns and xss.”
Then I recommend you do the responsible thing an email Kroc, or file a bug on the issue tracker, and possibly file for a CVE. If you have found actual vulnerabilities, those will swiftly get patched. If not by Kroc, then by me, because I am using NNF privately as
Also note that NNF is licensed under CC BY 3.0, and anyone should feel free to fork it.