In practice, Java 8 parallel streams are generally discouraged outside of raw number crunching, which is rarely where we need parallel speedup anyway.
When else do we need parallel speedup?
You should still read JCIP, it is still highly relevant in Java-land. Java 8 streams solved almost nothing in terms of concurrency (in fact they probably created more problems than they solved...). You should still be scared of concurrency in general, and particularly in Java. And you should definitely consider a different language with more sane and modern concurrency primitives if you really need concurrency.