At one time, PowerPoint did something quite useful for kiosk applications:

If nobody touched the keyboard/mouse/whatever for XX seconds, the presentation would automatically hop back to the first slide.
In other words, it'd automatically reset itself for the next person who viewed the kiosk.
I don't remember when this disappeared, but it'd sure be a useful thing to bring back.

How about an option in the Slideshow setup dialog:

Reset after: [textbox] seconds