Use SUM Rules Dimensioned by Users for Source Data not Dimensioned by Users

I recently posted a question on the forums in relation to a workaround for a bug in the LOOKUP formula. I wholeheartedly feel like the LOOKUP bug (where it doesn't work for parent items that are in the same list as the leaf-level members) should be fixed. And I recognize that there are some workarounds available (as identified by the responses to my forum post). However, I stumbled upon something that I think would be helpful as an option in the system.

Original community article I found: https://community.anaplan.com/t5/Anaplan-Discussions/Lookup-on-Parent-elements/m-p/1478#M2397

Forum post I made: https://community.anaplan.com/t5/Anaplan-Discussions/Lookup-on-Parent-Elements/m-p/43156/thread-id/4753/highlight/false#M4755

Idea Exchange post requesting a correction to the LOOKUP formula (please kudo that too!) https://community.anaplan.com/t5/Idea-Exchange/LOOKUP-does-not-work-on-list-parents-and-only-leaf-items/idi-p/34349

I think we ought to have the ability to have data that is not dimensioned by users, then have a rule that is dimensioned by users, and be able to sum the source data by that rule. This would allow us more flexibility in providing users views of data where thare are space limitations which prevent us from being able to dimension our output modules by all desired lists. 

The simple example I put together of what I am wanting to do is my original post in this thread:  https://community.anaplan.com/t5/Anaplan-Discussions/Lookup-on-Parent-Elements/m-p/43156/thread-id/4753/highlight/false#M4755