Makes a certain amount of sense, but I think there may be a couple of complications.
1) Referring to a child. There are often multiple children at same level, i.e., siblings. Would need a method to identify which particular sibling. As you traverse down, the subsequent number of subshapes could (not practically, though) grow at an exponential rate.
2) Chaining. Moving down would progress child to child (grandchild? greatgrandchild, etc.)
a.) This would always be relative? So, if I'm at the 3rd sub-level, say,a grandchild, at that level, the next one down would be its child, but to the upper most family member, it would be a greatgrandchild.
b.) Likewise, moving up would also be relative, no pun intended. Parent, grandparent, etc., but it's always from the perspective of the present location, or is it based upon an "absolute, external view"?
Seems like it could get just as confusing to try and keep track of where you are in the chain and to whom you want to point.
Perhaps an adaptation of a tree view, within or linked to the shapesheet, so you could point and click to get the shape reference? Hmmmm. That would be considerable development. But it could give you an instant visual...
Wapperdude