Using the -skipintro launch parameter caused the new UI not to load. I got a blue pulsing screen and ambient noises, but with no menu, whatsoever. The following link shows screenshots of the issue:
I added the -oldui switch and was able to launch with the old UI, however I had no character preview on the front page of the menu, nor was I able to create a default character. When I joined a server, my character had been deleted and I was a fresh spawn.
I verified the local content, deleted the local config files (allowing new default files to be created), Switched to 0.53 Stable and then finally deleted the local config files and the local content. I then reinstalled 0.54 Experimental and the problem persisted throughout.