It is an interesting idea to think about, but if it were to be put into practice it would affect the community of each site and then even if everyone goes to the new site, you don’t know how the groups will merge together, same for the staff involved.
In many ways I like that we have a small, in the grand scheme of the fandom, community here. I feel like I know everyone here and so the site has a certain atmosphere, that could be affected were many of the fansites to merge.
I think Tumblr shows that sometimes having a huge part of the fandom in one place is not always the best thing. There are a lot of really heated arguments there. The more people you have on a site the less of a true community it becomes.
Plus as you say each site has varying rules on how they handle copyright. We only post official links to legally view episodes, which has helped us in the past before when Nick contacted Jordan about Korra Nation before they fully announced it.