More specifically, he argued (and the recent and upcoming releases of most major frameworks agree) that rendering most content on the server with islands of client-side interactivity is the future.

That’s not necessarily a huge revelation, but the big difference from what people have been doing with PHP for decades is the level of integration and simplicity in mixing server-side and client-side code seamlessly so that a dev can choose the appropriate thing in each context and not have to go through a lot of effort when requirements change or scaling becomes an issue. I would say that this represents a new level of maturity in the “modern” web frameworks where devs can choose the right technology for every problem to serve their users best.