Systems research is more relevant than ever. You should take a look over the papers published at conferences such as SOSP, OSDI, EuroSys and HotOS. You'll see quite a lot of papers from industry giants. Lots of research OSs are also gaining traction[1][2][3]. I'd say that we're moving towards specialization right now, with a specific OS architecture for your usecase. OS research is far more than Linux right now.

[1] http://www.barrelfish.org/ [2] https://unikraft.org/ [3] https://mars-research.github.io/redleaf