I understand your point; but I'm struggling to see how this could be weaponized. Keep in mind, that these Dos compatible drive letters need to map to a real NT path endpoint (e.g. a drive/volume); so it isn't clear how the malware could both have a difficult to scan Dos tree while also not exposing that same area elsewhere for trivial scanning.

Wait until your learn about Alternate Data Streams…

> This all sounds like a wonderful way to write some truly annoying malware.

AFAIK you need admin priviledges to play with drives in Windows.