Google is announcing Android O Monday, and we'll find out what the "O" stands for. Usually it's dessert names, and it's hard to imagine it would be anything other than Oreo. That is a brand name, however, so Google would have to get permission to use it.
Android O will bring some new features, and many users will not get it. One of the biggest problems with Android right now is that companies who make Android phones and carriers that sell them are slow to update, if ever. The only people who will get it right away are Google Pixel owners, or those who have Nexus phones.