I think this is a great mod idea, however I think that maybe the worlds should be ordered by time period and you are slowly advancing through time for some end goal like if there was a world where you turned in a quest item from each world and the final boss spawned. We, yes I said we because I really want to help, would have to make each world a little more difficult then the next so that the items in each world are balanced. I would definitely like to help program the mod, however I don't have a Skype or an IGN if you let me help I can communicate by email. I have programmed a few personal mods but got bored with them after awhile because they lacked excitement. This mod shows true potential and I would be really excited to work on it. Thanks.
I just realized that you did not mention anything about forge. Would it be a forge mod or not because if you do not plan on using forge then I will not be of any use because I only know how to use forge.