You are correct, grynmoors. This is an addon that must be installed on each forum individually. So unless there is sufficient demand, most forum owners will not bother. Many forums still do not even offer something for YouTube, let alone anyone else.

The reality, for the moment anyway, is that you'll only be able to embed on forums that have html enabled in forum posts. Most forums have this turned off by default because there is a security risk to allowing people to execute html code within a post.