Creating such groups is already possible in both NodeCanvas and FlowCanvas (alas without comments, but rather only a title though).
To create such a group, simply make a rect selection as normal, and before releasing the mouse, hold down the Control keyboard key.
Here is the relevant link to the documentation about this 🙂 : [DOCUMENTATION LINK]
Please let me know if that is what you meant.
Thanks.
Gavalakis
