I went ahead and installed qtdeclarative5-qtmir-plugin and qtmir-desktop from wily-proposed and now the session starts as it should.
I think I'll leave this open until the packages transition out of -proposed in case someone else runs into this problem and can reference this bug. ** Package changed: unity8 (Ubuntu) => qtmir (Ubuntu) ** Changed in: qtmir (Ubuntu) Status: New => Triaged -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1485609 Title: unity8 desktop crashed with SIGABRT in qt_message_fatal() To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/qtmir/+bug/1485609/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs