I am definitely one of the users who appreciates having all three current modes: reading mode, source mode, and live preview mode. There’s a lot of interest in having a fully WYSIWYG mode, which I’m not opposed to, but I vehemently disagree with proposals to remove any of the existing three viewing modes. These modes benefit some number of users (I don’t want to venture into guessing user populations), myself included, and removing functionality would actively harm that population of users.
I do think that switching between modes could be clearer or more streamlined, although I don’t have any concrete suggestions here. Just some way to have a single UI element to toggle between source/reading/live preview maybe? It’s a tricky thing.