My team is hiring. For example:
https://careers.microsoft.com/JobDetails.aspx?jid=7594&lang=en
As the job description says, we are focused mainly concurrency & parallelism at each layer of the system: kernel-mode, user-mode, frameworks, languages, compilers, ...
The sky is the limit and nothing is off the table. I've never had so much fun in my life as I am having right now, and couldn't imagine a better group of people to do it with. I think this is what NT must have felt like.
If you're interested, email me at joedu AT microsoft DOT com, or apply via that link.