As of snv_109, all attempted (wizard-based) GUI installs fail as follows:
Discovering additional network configuration...
/usr/X11/bin/X /tmp/root/usr/openwin/bin/Xsun is not a valid X server
I don't think the CR 6805131 Xserver script changes handle the "/tmp/root" prefix on an otherwise "known" X server binary, when checking that the path of the server is recognized. Alan Coopersmith also suggested CR 6610692 could be involved.
Gui installs on x86 haven't worked since build 107. I did try a few anyway, and instead of the typical gray screen and hang, I got the following message, which is similar to what sparc is seeing:
/usr/X11/bin/X: /tmp/root/usr/X11/bin/Xorg is not a valid X server