Since I work alone I suppose I'm not up to speed on what defines a single page app but the apps I've been building with PouchDB, jQuery, and Bootstrap run in a single page.
"Stateless requests Traditional web servers are built to be stateless. "
True, but "apps" should be designed to be self-contained (i.e. all the user navigation is done within the app UI, not the browser UI).
"The browser knows how to deal with a traditional architecture If you go with the SPA route, you’ll always need extra code to emulate trivial browser features."
That's a pretty trivial problem and browsers don't really solve that, nor should they.
"Fewer, more mature tools Avoid the Javascript fatigue by not relying so much on Javascript!"
The apps I'm building are almost entirely Javascript. I see that as a good thing. What little I do on the server side I do with Perl, which is something I've been doing since the `90s, so I can feel "traditional" doing that if it helps me sleep at night.
"SEO for free Single-page apps have to add extra infrastructure and code to make sure they can be indexed by crawlers."
This is not so difficult to address and in some cases it's not even a consideration. In the case of a "blog" app you can simply assign a url to a post and deliver a page built on the fly specifically for it. Google can parse that.