I'm veering into the pedantic here...
Rails certainly can work fine without Javascript. As you say in this booking example, you can certainly just re-render the page completely on the server (even if it is 'icky'!)
However to really use rails without javascript you would have to be careful to avoid the many standard features which are implemented using js.
e.g.
<%= link_to "test link", test_path, method: :post %>
This submits via POST normally, but via GET if you disable javascript in your browser (or if you don't include the standard js includes)
When I started writing Rails, it was normal to consider that a meaningful proportion of your customers would not have js, and write the app to handle that case.
Today, I certainly wouldn't waste time coding for the 'what if they don't have js' scenario.
cheers,
Rob