One item on the future plan is selection of multiple tracks. Once this is implemented, all track commands such as delete or grouping would be applied to all selected tracks. I think this is a better way to support more flexible track organization, rather than adding new commands for grouping multiple tracks.
One trick I normally use when I want to put several tracks into a group, is to collapse the parent group, increase the group level of the parent group (the entire group is affected), unfold the parent group, and decrease the group level of the parent (only the parent is affected). Thus you have added an extra unused level between the parent and all its children. Then you can easily insert a new group track between the previous parent and the sub tracks.