Don't quote me but I believe this will be an option in Lumafusion to some extent. I say that because you can browse all your media on the external drive and mark selections for use in your project. On the Gnarbox external drive today, I believe when you add this selected footage to a project, Lumafusion only imports the selected range and not the full media file which obviously saves some space.
Not sure if other external drives will work the same way for importing only selected footage under iPadOS in Lumafusion but being able to browse all your footage directly from the external drive in Lumafusion will work.
I cannot comment on other editing applications but if you are even remotely serious about video editing on the iPad then you should be using Lumafusion!