> That is like telling students to never do a PhD thesis on superscalar out-of-order execution, stochastic gradient descent, or UDP.

No decent PhD advisor would let their PhD student base their PhD thesis on such well-known concepts: a doctoral study programme is a journey into something never-seen-before (with a very high likelihood of faling and shattering your life). Anything else is failure.

(Obvious exception: either he or the PhD student can convince the other one that there could be something really, really deep in, say, "superscalar out-of-order execution", "stochastic gradient descent" or UDP be found that generations of researchers overlooked, and which once discovered might necessitate rewriting all the standard textbooks about this topic).