I'm quoting the admin of
whatismyip.com,he had stated this in quora :
The WebRTC vulnerability could give away your real IP address. Even if there were no vulnerability, it could come down to how the VPN is set up. Are they using tunneling? If not, then everywhere you surf could see your real IP along with the IP of the VPN. Is the VPN including your IP in their header?
You can of course disable WebRTC.
Even if the VPN were locked down and no trace of your IP were leaking, this doesn't mean you can commit nefarious acts online without getting found out. There are log files on every server. The amount of time logs are kept varies. With enough resources and legal action, log files from VPNs could be turned over to authorities. Once they see your real IP, they simply subpoena your ISP and will find out who you are. Realize that it can be more complicated than the scenario I use above, but my example is to simply help you understand that you're not truly hidden online.
A good VPN doesn't keep logfiles, so there's nothing to subpoena.
Obviously not everyone on this forum is a tech savvy bad ass to be as careful and take all measures for revealing your real IP, but I just realized that it just cannot be implemented on this forum, as I began reading more on it, seems to be really hard to implement and theymos alone will almost find it impossible to do such.
Aside from technical possibilities, theymos values user's privacy. That alone is a reason not to do this. And in the end I don't expect it'll stop spam anyway, it's the core business for spammers.