Today Google announced it is deprecating it's AJAX Crawling Scheme. Google feels confident enough to rely on their bots executing your site just as if a real user were driving it in the browser. This in large part is due to the advancement of things like nodejs and phantomjs.
This decision means several things to the single page application space, the escapefragement_ becomes moot and you may not need a core site any longer.
What was the Google AJAX Crawling Scheme?
If you read my High Performance Single Page Application book you know I spend a decent amount of space discussing what this specification is and how to implement a dance between the client and the server. In essence you should have a way to serve the page content as if it were 2008, from the server.
Fortunately this can also be used to support legacy browsers like Internet Explorer 9 and old Androids. This is accomplished by doing some simple feature detection and redirecting the user to the core site. The core site is that legacy site.
So What Now?
This announcement is good news, but don't just go pulling your existing site infrastructure just yet. I mean it still works and supporting these old browsers might be important. But come January Microsoft ends support for legacy Internet Explorer. This means, crossing fingers, we can start phasing out any support for these old, outdated browsers soon.
As for new construction I say think about whether you want to invest in the core site experience or not. It may not be worth your time investment. Just realize that you may be excluding a part of your potential audience.
Personally I have been phasing out my core site investment over the summer. Line of business applications should not need a fall back for legacy browsers unless your corporate IT is about 6-8 years behind the times. In other words if your company or target employees have modern browsers you can fully leverage single page applications.
I am glad for Google deprecating the AJAX crawling guidelines. It means the web is moving forward and that rich web applications should become the standard. So go froward and build your rich web experiences and try to start deprecating your time and effort invested in supporting old browsers and search engine spiders.