Hey, this looks really nice! And if these ?... names are taken by apps (which should be) it would imply that we may have also other "drive letters". For instance whole words.
Well, the syntax is a bit more complicated, for example \?\c:\reactos, but it would be possible to implement longer drive names this way. Of course there are some limitations. The API function GetLogicalDrive() is only capable to return a bit mask of existing drive letters. (max. 26 out of 32) But this is already superseded by GetLogicalDriveStrings(), which would be compatible to "drive words".
Regards,
Martin