There actually were some WebRTC based plugins before NodeBB 1.0, but I don't think there are any working ones now.
Adding it would require creating a new plugin, so it would certainly be complicated. However, it's definitely not impossible and it's probably not that hard nowadays, because you don't actually need to handle anything with voice or video - as others had done that before probably better that you would. If you or someone from your forum would actually want to try creating such plugin, integrating Jitsi Meet might be one of the best ways to do it.
Jitsi is open source, has an API for integrating it into other webapps and also allows for self-hosting (which not only means better control over the installation and data, but also the number of users will be limited only by how powerful your server is instead of being capped at 75 like on meet.jit.si). And since it's a videoconferencing platform it will also have features connected with that like screen sharing or recording the meeting.