@edi
Yes I have also worked on doubango html5 webrtc2sip it is nice, however it requires some configurations by the end user in terms of sip account name and other stuff.
Also there is another application html5 based but nothing to compare with webrtc of freepbx (must know that this is voice only no video is supported yet) the html5 based supports video (not consistent, mostly works on Firefox)
The aim is to make it zero config for the end user, hence I suggest to stick with voice only sip integration if someone is willing to invest sometime on this feature.