Looks like xubuntu-default-settings wasn't migrated to using /usr/share. I've fixed that in lp:~robert-ancell/xubuntu-default-settings/lightdm.conf.
The reason lightdm wasn't starting was (from lightdm.log): [+0.58s] DEBUG: Seat: Creating greeter session [+0.63s] DEBUG: Seat: Failed to find session configuration lightdm-kde-greeter
i.e. It's been configured to run lightdm-kde-greeter and you don't have that installed.
Which I'm going to assume is in /etc/lightdm/lightdm.conf or you have modified /etc/lightdm/lightdm.conf.d/10-xubuntu.conf.
Looks like xubuntu- default- settings wasn't migrated to using /usr/share. I've fixed that in lp:~robert-ancell/xubuntu-default-settings/lightdm.conf.
The reason lightdm wasn't starting was (from lightdm.log):
[+0.58s] DEBUG: Seat: Creating greeter session
[+0.63s] DEBUG: Seat: Failed to find session configuration lightdm-kde-greeter
i.e. It's been configured to run lightdm-kde-greeter and you don't have that installed.
Which I'm going to assume is in /etc/lightdm/ lightdm. conf or you have modified /etc/lightdm/ lightdm. conf.d/ 10-xubuntu. conf.