This is just in alpha review at the moment, there is nothing yet in production.
In the beginning of the below video presentation, Dan Abramov talks about how web apps, in general, have 3 main goals, to be fast, cheap and good. The rule of thumb so far is to have 2 of 3, but Dan explains how all 3 can be achieved with React Server Components.
There is a demo of an actual application where you can see React Server Components in action.
Will Server Components replace SSR?
No. They are different. In fact, at first, React Server Components will be experimented with via frameworks such as Next.
Want to learn more?
The video presentation: