I would also love to see markdown if y'all can figure out how to make it work well. But... I think the reason it isn't implemented is fairly obvious: Markdown has 2 distinct modes, authoring (with markdown syntax) and viewing (with rendered styles). Notes are meant to be edited and read and changed and used as you go. "Note taking" is not the same thing as "authoring", and writing Markdown is definitely a form of "authoring".