Making a major change like that in a stable point release would be unusual for Debian. Since Debian 8 (jessie) shipped with X as default, the 8.x point releases do the same. If that switch happens, it'll be with the release of Debian 9 (stretch).
Right now, the only Linux distribution ships Wayland display manager by default is Fedora 25 (I am running it on an old Latitude D630 with NVIDIA GPU -> KDE Plasma 5 ;-).