If you are like me, your initial reaction should be, of course! After more thought and consideration, however, the answer is not quite so clear. Besides the fact that there aren't a lot of client side web apps that care about SEO, the issue is that a large majority of those have other issues besides simply using the fragment spec. Namely, initial page load time, a good internal site structure and other on-page SEO best practices.
The best (and one of the only) examples of a client side web app that does a good job at SEO is Alex MacCaw's monocle.io
. Unlike most client side apps, however, Alex has done a great job of ensuring the initial page load is lightning fast and he has implemented many other SEO on page best practices.
Also consider that Google engineers have been publicly saying for some time that if your client side app is user friendly than it will be search engine friendly. While I think it is not as simple as that, it does make me start to wonder if when all other secondary issues are removed (i.e. using pushstate instead of #!, fast initial page load, etc.) then perhaps the Google search algorithm may not be too heavily weighted toward server rendered websites.