Eric Bidelman has created
an example that does pretty much exactly what you describe (
you can see it running here). It uses
core-pages to respond to a URL change by displaying a different template. The URL change is coming from the
flatiron-director element. The pages are already loaded so it's quite snappy, the one thing it doesn't do is load additional pages using ajax (which you may or may not need). We're planning to clean this example up and present it as a more thorough explanation in the future, but if you want to get up and running now, you can just take Eric's code and modify it.