I can see the relevance to single deck, but wouldn't you have two keycards in double deck, one from each deck? So which keycard is the one I am waiting to act upon ? And by the time you find a dealer with (assumed) consistent riffles, they are either taking a break or it's the end of their shift.
I suppose an intimate familiarity with the exact shuffle procedure is required. And a hell of a lot of scouting.
Still learning, still exploring