Trev, over at the Model 3 Owners Club YouTube channel has released a new video that shows how to get to what appears to be an entirely new configurator for Model S. You start by typing in www.tesla.com/build/models, then stop the page load before it completes. There's a vastly simpler array of bundled choices with the option of reverting to the existing configurator for a custom config.
Which is all very entertaining as a potential preview of what's coming (no guarantees, YMMV, etc.); but then I thought to try www.tesla.com/build/model3. It doesn't do what you'd hope, but it does bring up a new, 'hidden' page that's a different way of reaching the existing configurators.
Of course, all this may change from hour to hour as Tesla's web designers do their thing.