To download the other ones you need to make a folder in the versions folder for minecraft and put the client and JSON file for the versions in there. They all need to be named the same aside from file extensions. Once you do that, you will be able to choose that version when making a new profile with the minecraft launcher.
A new dimension would be cool; but I highly doubt it is. I don't think people want more dimensions either; if you want dimensions play modded Divine RPG. That was a fun scenario for quite a while, but I really don't like Minecraft to be a dimension game, with tons of dimensions