I am a Stable branch user of KDE Wayland and I’m also concerned about the default session being changed.
When the Stable branch is eventually updated, on first reboot, will I be able to just choose a Wayland session at that point? Of course, I’ll have to remember to check. And would prefer that the default not be changed. 
It appears this update renamed the Plasma X11 session, breaking some things (such as last remembered session and autologin settings).
In my case to fix the autologin I had to edit the /etc/sddm.conf.d/kde_settings.conf file and do the following change:
--- original/etc/sddm.conf.d/kde_settings.conf
+++ /etc/sddm.conf.d/kde_settings.conf
@@ -1,6 +1,6 @@
[Autologin]
Relogin=false
-Session=plasmax11
+Session=plasma
User=mysak
[General]
Stable users on Plasma 5 use the old session filenames (plasma.desktop for X11 and plasmawayland.desktop for Wayland), testing/unstable Plasma 6 users had the new one (plasma.desktop for Wayland and plasmax11.desktop for X11).
We just reverted the names back to Plasma 5 days so old users won’t switch to Wayland on update and new users will get X11 by default. So this change was specifically made so Plasma 5 users won’t feel any difference (X11 stays X11 and Wayland stays Wayland). I couldn’t even think that this will push existing Plasma 6 Wayland users to X11 (but now it sounds logical, yeah).
It’s good that we caught this behavior on testing. In future when we’ll make Wayland the default one we’ll consider doing some magic so people won’t switch to Wayland automatically on stable…
X11 timeout already started.
I’m not saying we’ll stay on X11 for another decade or so.
Good decision… i saw already people run into issue, because they had nvidia GPU and running into problem’s on Manjaro/KDE from a fresh Iso installation.
Default should be X11 till most problem’s are sorted out, you guys doing a great job with this changes, thank you 
What issue and that’s Wayland’s fault how?
If every distro and various devs had this backwards mentality, then it would take another 100 years.
Plasma/Wayland Known Significant Issues
For your information. 
X11 has much severe and unfixable bugs which no party is wanting to spend money or effort to fix them.
Wayland bugs are now being hammered by the whole KDE team with the help from other Linux/Wayland communities.
8 posts were split to a new topic: Trouble switching to testing branch
I honestly don’t undrstand how putting a lot of unaware users into a half-baked environment would help the development.
Which is really great but the X11 list you linked is like 2 times shorter than that of Wayland.
Every big project should always have a big list of opened bugs, if not then the project is not healthy because it doesn’t have a wide base of users, so it’s a technically dead project.
Bugs’ severity is not compared by the numbers, but if you have the means to make fixing them doable. For X11, no party/company is willing to pay for even patching that old dying beast.
They prefer to reinvent things with Wayland to gain more control while adding new features instead of wasting time debugging that complex code accumulated over years.
Thanks for the seizure warning. I’m glad I read the forum announcements.