A few weeks ago, Mark Shuttleworth, now CEO of Canonical, announced that the Unity desktop shell would be abandoned in favour of GNOME. While we were told that GNOME would be used by Ubuntu 18.04, we weren't sure whether it'd be included in Ubuntu 17.10, the next release. Following a meeting on IRC, we now know that GNOME will ship by default in the next release.
For those of you invested in the Unity desktop, Unity will be installable on Ubuntu 17.10, but Upstart (a system alternative), Ubuntu touch packages and Unity 8 are likely to be removed from the repositories, marking an end to Unity development. Due to the open nature of Linux however, there will be developers who no doubt fork Unity, rename it, and continue to develop it much like the Linux Mint developers did with GNOME 2 when they created MATE.
Aside from GNOME, a Wayland session will be included in the upcoming release side-by-side with an Xorg session. It's still an unanswered question as to whether the LightDM login manager will be included or whether Ubuntu will ship with GDM which is present in the upstream GNOME desktop.
While the changes may not yet be included, eager testers can download daily builds of Ubuntu 17.10 from Ubuntu's website but they should be considered pre-alpha quality, so some problems could arise.