Visual Studio Code worked really well for us as well, it worked well with all our polyglot services and the .Net core integration had great cross-platform developer experience (to be fair, F# was a bit trickier) - actually, each of our team members used a different OS (Ubuntu, macos, windows). Our production deployment ran for a time on Docker Swarm until we've decided to adopt Kubernetes with almost seamless migration process.
After our positive experience of running .Net core workloads in containers and developing Tweek's .Net services on non-windows machines, C# had gained back some of its popularity (originally lost to Node.js), and other teams have been using it for developing microservices, k8s sidecars (like https://github.com/Soluto/airbag), cli tools, serverless functions and other projects...
What was the benefit of using F# to impelement the rule engine processor?
F# type system is very suited for representing AST (https://github.com/Soluto/Tweek.JPad/blob/master/Tweek.JPad/Ast.fs). Additionally, F# pattern matching, currying and type safety are useful for control-flows, composition and correctness.