Yes, that's pretty much what I had in mind. I guess the reverse would be to right click on the group and select Add Node to Group from that context menu, and then select the node either by clicking on it or from a drop-down menu.
I'm not sure this would be as simple, but alternatively, when a group shape is displayed as a faded backdrop to its member nodes (the default), it would be nice to be able to drag the desired node to within the group shape's border, thereby adding it to the group. This would probably imply that non-group members can't be within the group's shape, whereas it nodes of any group can be anywhere on the viewport in the current version.