[Bahamut]

Using PhantomJS to prerender is not a viable solution for everything - for example, fast updating content like forum threads.

[Illniyar]

Why not? it's not like google and other crawler bots crawl your site every second, we are talking about roughly once a day.

And even then, there are solutions to do PhantomJS rendering on the fly, it might be a bit slower, but shouldn't be drastically so - some of the SAAS solutions I mentioned already provide such an option.