I think you're misunderstanding what a single page app is. If a single page app is degrading gracefully when Javascript is turned off then it is probably not a single page app.
A web app where this is just one HTML file but the JavaScript gives it the feeling of being a whole site (client side template rendering, etc). I think in essense a single page app is one where there is no server side temp laying.
What do you think of the single page app you've described with multiple html entry points?
Say / responds with the homepage as per usual
and /feed responds with a different html start point, but the same application code.
Using this technique you could create a site that responds to multiple urls with html and at the same time creates a SPA experience using a single js application (say, with backbone for example).
