Is the GUI wallet able to automatically check for updates and advise users to download the latest version, or will future updates be announced elsewhere?
New releases get tagged on the github page, which is currently the freshest source of info on development progress.
Shortly after, downloads would be found on the "official" project site https://getmonero.org
Also, the Monero sub-reddit usually has important information stickied as the first post.
With this kind of software, it is probably not a good idea to implement auto-check as it could become a security vulnerability.