I couldn't find any previous suggestions to this effect, so I mocked up a few visuals to aide in the suggestion here. When attaching a link to a local folder that exists on either a LAN or local HDD but is NOT within the internal folder structure of TheBrain itself, how about displaying those files in a basic file explorer with some basic layout / zoom support?

Some Example Code For C# ... I think TheBrain is using C# right?
As Is:
Folders As-Is.png 

Support File Enumeration.png 

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