Where can we find out what the expected changes for the next version of Ubuntu are?
One way to keep track of news of new features is to read one of many well-known blogs or news sites that are Ubuntu-specific during each release's development cycle. Examples include OMG! Ubuntu and Web Upd8.
If you don't mind wading through mounds of technical stuff, there are blueprints for Ubuntu at Launchpad that could offer some clues as to what will come in the next release.
Lastly, there is the Ubuntu Contributors Channel on YouTube, which keeps a large collection of video recordings from the Ubuntu Developer Summits, as well as interviews with some of the developers.