@Jylocasin: Spend a few hours and try to assign a user to multiple roles. In the future you will thanks me. :)

Imho, user subtypes could work in an hierarchical role system, which would make sense in Elgg's action context. I think that's one of the approaches I will attempt to explore in hypeApprove for 1.8

I created the ScopedRole library with the hope that it could be used to create a role system in Elgg (or other frameworks that lack it). You could associate users with different roles in different contexts, like a site or a particular group.

The hard part is combining role querying with the existing ACL system. Given a list of entities from a get_entities query, you'd have to do quite a bit of querying if your view had to optionally show an edit button.