What are the recents topics of research that combine both systems research and theoretical computer science?
This might not be what you mean by "theoretical computer science", but there's some rich interaction between Programming Languages Theory and Distributed systems going on with Session Types. They basically are a way to use type systems to specify communication protocols, increasing safety in distributed languages.

For example, The Imperial Mobility Group has many publications in session types, this should at least get you started on finding research in the area.