I suspect this isn’t a quick and easy one, but I’ll throw it out there anyway…
How about being able to define a sort order when creating a multi-relation?
For clarity, I don’t mean being able to sort an Inline List that’s using a multi-relation as a source (which of course we can already do). What I mean is being able to define the ordering of a multi-relation as part of the column configuration.
So when you create a multi-relation column, you have an opportunity to define a sort column, and the ordering of the returned rows will be based on the values in that column 
PS. The use case for this is in the topic I linked to.