I just came across this truly incredible design on the German Knife Forums. It's a custom by Scorpio Designs, called the ShapeShifter, and the first thing I thought was "I want one." The second thing I though was, "this would make a great Spyderco Collaboration for the Slipit Line."
Basically, instead of having the knife fold out of the handle, the handle "shapeshifts" into a guard for the blade. When open, it doesn't appear to have any locking mechanism, but because the handle is "locked together" by the hand, it looks like it would be every bit as secure as a lockback - your hand would have to completely open for the blade to close.
I think if it were possible, this would be a real game changer for the Slipit/International series. You would have a non-locking folder that's every bit as secure as a lock, and because it doesn't appear to be one-hand opening, should be legal pretty much everywhere from NYC to Denmark.
As someone who does a fair bit of traveling, I'd love to have a Spyderco version of this that didn't cost $800