Since it's a long weekend here I've decided to bite the bullet. The new UI is now live as the default.
If you need the legacy UI you can temporarily reach it at:
... but I'd appreciate it if you let me know why you're switching back.
Note that I have not yet replaced the iframe.htm stub, in order to give the new UI a few days to bake. Eventually that will become a redirect to just http://travellermap.com/ - the main page detects that it's running in an iframe and hides the UI.