How about a new type of Repeater for shape groups that looks pretty much the same as the existing one, except that values in it's Transform properties are not applied cumulatively, but rather have their expressions evaluated individually for every copy of the shape?
So if I add a random expression to the repeater's Position property, I get a bunch of randomly positioned copies. Ideally we'd get expression access to something like repeaterIndex (like textIndex in text layer expression selectors) but even without any new syntax it would be amazing. I can already imagine making a growing vine which automatically sprouts leaves as it gets longer.
Might save someone jumping over to Cavalry, and could provide some new possibilities to MGRTs too.