I've been planning 2 new leagues in different universes for a few months now!
I don't want to say too much yet, but one is in a future fictional universe and the other is in a present alternate universe. Both have background stories.
I have some possible structures already in mind (final depends on what we're able to do in the end) with some team names and their color schemes already picked out. I've already picked most of the settings we see in the existing version, but of course there will be more to choose from in the newer version.
The only downer so far are the schedules. I'm very picky with what I want. I was going to go ahead and do them up, but without a fast way of getting exactly what I want and with the format possibly changing I guess I'll just wait on that.
With the newest version soon on its way I just can't find the interest to play with the old game. So I plan for the next.
My only suggestions would be to keep your plans flexible and don't do too much with things that could very well change.