Just an update for everyone. Nested groups or Slices have been a long-requested feature and we understand the need for it from your use cases.
We are currently reshaping the experience for developers to build Pages Types and Navigation Types (Headers, Footers etc..) in Slice Machine, and this topic is part of the things that we want to improve, although we do not plan to include this until we come up with the first versions of Navigation Types in Slice Machine.
Once we release Navigation Types in Slice Machine we'll move on to the other use cases we'll keep you all updated here.
Thank you for your patience and passion about getting these features out.