I really hope not. Rails is awesome and I love it to bits, but I will hate to have to use a framework that is massively invested in Ajax/Pjax. The reason for this is simple: UX. Companies don't seem to understand that there's more to the world than just America and America's top-notch Internet [1]. A lot of web traffic comes from places where the connectivity is simply shit and interfaces like Quora, GMail, Twitter et al that have so much functionality with server-side JavaScript as a prerequisite make it seriously difficult to have an enjoyable experience more often than not. If you've ever tried to access Google Analytics on a 1mbps shared connection in a relatively populated office, you'll know what I mean.

Yes of course Ajax and the interactivity and convenience it offers are awesome, but they come at a massive expense, and this is something that will be very saddening if Rails starts considering it as a major part of its core sooner rather than later.

[1] Alright so it's not just America, but my point stands.