Maybe a completely new dimension with a new boss. o possibly a new mob. It would create a brand new adventure. Maybe they should add multiple bosses in different dimensions - so the 'story' of minecraft doesn't just end with the ender dragon. I don't know... maybe they could add a boss for each mob (like endermen have the ender dragon). For example, to get to the 'ghast dimension' o something tu could collect a certain amount of ghast tears to activate a portal to enter the dimension; and so on for maybe blazes, zombies, skeletons etc. I'ts just an idea. I'm not very creative with ideas like these as such :) haha. But yeah, i'd probably add más 'missions' as tu could call them to do if tu want. Of course it would be optional just like the end. But hola ho, haha :)