Tenth planet? Brown dwarf companion star? Simple statistics?

Maybe there once was a smooth distribution of mass in the outer solar system, but the outward travels of Neptune pushed more mass out to the edge, creating the "Kuiper Cliff"?

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Maybe gravity is not asymptotic, but stuttered. Or maybe there is a Weak Gravity force in addition to the normal (or Strong) Gravity force. Then again, Ice Pirates might steal from the edges for the sake of stealth.

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Could the KB be analogous to the rings round Saturn etc., with planets and larger KBOs shepherding the smaller material?

We know very little about the fine stuctures out there and I personally wouldn't want to go inventing any new forces until we know more about what we are dealing with. We may well find that there are several defined 'cliffs'.

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Or maybe there is a Weak Gravity force in addition to the normal (or Strong) Gravity force.?
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There are definately gravitational sweet spots that exhibt different strenghts in force over the considered normal.

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True. One could consider the asteroid belt to be a similar 'cliff' or zone of debris. Gravitational interactions with stars that passed close to the Solar System millions of years ago may also have played a role ('close' in this case being around 1-2 ly).

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