Kristian Høgsberg announced the Wayland/Weston 0.99.0 releases to get some last minute testing before declaring version 1.0. There ended up being more API and protocol changes at the last minute, so additional testing was warranted. "At this point I've pulled all patches from the list and I feel that the big changes have settled in pretty well. We now have responsible error handling, we have a well-defined atomic update mechanism and event dispatching is thread safe. I've been very happy to see the effort and the amount of patches on the list recently, and without that we couldn't have wrapped up the protocol and client API changes in time."
The error recovery for Wayland is detailed here along with the Wayland thread-safe work.
Due to the last minute API breakage, he's letting the 0.99.0 snapshots bake for a week and meanwhile he plans to spend time porting clients and tool-kits to the expected Wayland 1.0 interfaces. Should nothing go wrong, Wayland/Weston 1.0 will be officially released on 22 October.
Wayland 1.0 isn't going to mark the point at which everyone is going to stop using X11/X.Org, but rather it marks the point at which Kristian and other Wayland developers will begin ensuring backwards compatibility and stability. It will still likely be a few more Wayland 1.x releases before this next-generation display server is ready to take on the Linux desktop.
The Wayland/Weston 0.99.0 release announcement can be seen on wayland-devel.