The Wayland change for Fedora 21 is about better supporting GNOME Wayland sessions. Fedora 20 already brought experimental GNOME Shell Wayland support while Fedora 21 is building upon more polished support thanks to upstream improvements landing with GNOME 3.14 due out in September.
With Fedora 21's Wayland support work it will focus upon addressing user-visible regressions and clearing up other shortcomings of GNOME on Wayland compared to running it upon the X.Org Server as it's been done over past years. It's not for sure yet that a Wayland-based environment would replace the X.Org Server by default for Fedora 21, but at least the support will be in good standing.
In time for Fedora 21 will also be X.Org Server 1.16 which integrates basic XWayland support for running X11 applications atop Wayland without requiring separate X.Org patches.
The Wayland F21 changes were approved today during the weekly FESCo meeting. Besides improved Wayland support is also many other Fedora 21 features.