The Symfony Finland site has a post about Angular 2, its server-side rendering support and how Symfony can fit into the picture.

At the ng-conf event in May 2016 there were sessions discussing how Angular 2 can support server side rendering in various platforms. If you're working on a project running on Node.js, then Angular 2 is a native citizen. For other options like ASP, Java and PHP there are a few options on the table.

[...] Later during the ng-conf more details on the Server Side Rendering (Universal Rendering in Angular lingo) can be implemented in different environments to improve first page load experience. [...] The downside of these approaches is that you need to add additional complexity either by adding a dependency to an external service or require a rather exotic PHP extension at this point.

Instead he suggests using Twig along with the Angular 2 template compiler and some custom extensions to the base templating to format the output as Angular is expecting it. He talks about how the current backend rendering of templates could easily be translated to this handling. He also suggests that even just partial server-side rendering might be enough to help with the performance of the application.