Currently it's possible to set security permissions on a business unit hierarchy, however many organizations are matrixed and accessing CRM data. So we want to be able to set up security permissions (create / read / write / delete / share etc) on more than one hierarchical dimension.
For example we have product lines reporting to business units on one dimension and we have sales reps reporting to teams reporting to regions on another dimension.
We want to be able to have matrixed security in multiple dimensions.
This could be achieve with some other row-level security and filter conditions on the security model such as adding a fetchXML condition to a security profile or a user profile (where territoryid = "Americas" for example).

We looked at using record sharing with teams etc, however the PoA table will grow massively, and sharing / unsharing, including child and grandchild records become unwieldy very quickly. Also dealing with children created after the parent is shared, and orphaned POA records after some unsharing scenarios.