Velojet, A simple avatar chat program like ThePalace, IMVU, could easily be done through simple chat-like messaging between clients. I made one in Construct Classic with SciDave's plugin here: Pixel People Online
There's no real "cheating" possible (just remove kick commands), but it allows people to hang out and socialize.
Fimbul, I know, but I really want it included with Construct 2 so that anyone could use it if they didn't know to come to the forums, or so that they even know the plugin exists.
I guess a good method would be to highlight some types of third party plugins that exist in a list on the C2 download page, and forward a "See more plugins" link from there to a list of complete plugins on the forums.
I definitely agree on the point of exporting a serious node.js being too low priority, anyone making an extremely efficient multiplayer game with proper authentication will likely be able to do that themselves in good time.