It doesn't give you the collapse/expand function, but you can sort of achieve your desired result with standard member expansions. For example:
A#SelectedMember.Member.Descendants.Where(Text1 = Predicate)
A#SelectedMember.Member.Base.Where(Text1 = Predicate)
Thought I'd mention the above as a potential solution until your enhancement is built.
Edit:
You can force an expander to appear with the above member filter by making this a nested member. Meaning, put an arbitrary member as the first selection, then put the above filter as the 2nd item in a list. It will display with an expand/collapse + sign.
Thank you for the proposal, interesting but still doesn't meet the requirement as between my top member and the base members where this filter applied, there are some intermediate parents, which in your solution will all display as flat below the "A#SelectedMember", so I don't have either the indentation, and more important the collapse/expand on each parent
