In pretty much every game creation system that has online functions, the GAME is the server.
That is, one player presses "Create", notes the IP, other people join.
A game lobby is often set up by the developers, and that would require a dedicated server, but that would be the worry of the developer of that game, not Scirra. All we need is a plugin that lets you send TCP/IP messages. Something easier and sleeker that might need a server of its own might be introduced later, but right now that's all we need.