​A few suggestions.  This name is too specific.  If such an option is introduced it could just be named

mouse-drag-and-drop-region-cut-flag and any limitations could be included in the doc string, as they are already.  Then

if its behavior were modified in the future, the name would not need changing.

But the option, mouse-drag-and-drop-region, already exists and does a bunch of things that control cutting and copying

of the dragged region.  It would make sense if this setting could somehow be integrated in there (one source of truth)

so there were no need to add a boolean just for this one aspect of regional drag and drop.​