The fact so much hardware these days is running a full real-time OS all the time annoys me. I know it is normal and understandable but everything is such a black box and it has already caused headaches (looking at you, Intel).
It's about the dominant unholistic approach to modern operating system design, which is reflected in the vast number of independent, proprietary, under-documented RTOSes running in tandem on a single system, and eventually leading to uninspiring and lackluster OS research (e.g. Linux monoculture).
I'm guessing that hardware and software industries just don't have well-aligned interests, which unfortunately leaks into OS R&D.