The funny thing is Hammerbacher worked on trading problems which have tons of super fun CS problems even if it is a bit nihilistic making rich guys richer ... then founded Cloudera, which, I dunno, seems pretty "beige" as far as CS goes. Didn't realize he did a stint at FB. That could suck the life out of anyone.
Physics has the same problem. Upwards of 20k people in the APS... most working on very obscure problems spraying "shittonium on silicon 111" or making no progress in various theories of everything.
Still plenty of important and interesting problems in CS, some of which I've been lucky enough to work on.
Blockchain stuff is pretty useful and interesting, though it could all fall apart with some breakthrough in crypto.
Machine learning is mostly used for stupid stuff like getting people to click on ads, but there's lots of interesting use cases for it which haven't been explored yet.
There's also a lot of work to be done on the core tools used in ML; while everyone babbles about deep learning, boosting, PGMs and topological data analysis still have a lot of low hanging fruit IMO.
One that people don't think about enough: non-standard computing architectures. Quantum computing hasn't produced anything of note yet, but it's hardly the only potential area of research here. Simply using stuff like old school Harvard architectures has tremendous implications for security (no more buffer overflows, yo), but nobody bothers thinking these things through and implementing.