Here is a thought that I've been playing with over the previous weeks, but I'm not sure if it's viable. What if instead of making a website, you created an entirely mobile application? My theory is that you could eliminate the need for creating accounts since most people only usually use one device. You can still have all of the mechanics for inviting and creating teams, because that would be native to the system. All you would need to do is store a UUID for each user.

There are a few drawbacks to this approach such as a user losing their device. Essentially all of their history would be lost with it unless you used something like CloudKit to back the users info up. The problem with an API like CloudKit is that it isn't cross platform (yet). A user with multiple devices could join the same game, but I don't see how that would stop users with multiple emails from accomplishing the same thing.

Just something I was thinking about, but I do agree with not creating more accounts. There needs to be a more elegant solution.