That sounds exciting! I like the idea of gradually making the nights more challenging instead of throwing everything at players right away. Have you already decided what the first boss might look like?
Currently just like the zombies we ll have skeletons, spiders etc for the mobs, and the elites or bosses ll incorporate those same types. So its not going to be like scaled version of the same mob but incorporate the same type and theme of it and have unique mechanics alongside it is our vision.
Overall we want to follow the road for the minecraft authenticity, (keep that in mind these are very late stage ideas after the release), we want to introduce new worlds, for example imagine the environment is fully underwater with whole new features and day&night content with core gameplay staying the same, or nether like world with the same idea etc.