Yes, I have seen it.

But note that it does not and cannot be readily extended to allow dispatching based on what prototype coercion finally made the code not a syntax error. Which is what was being asked for.

So it doesn't solve the problem at hand.

Besides that it is a performance hit, and there is considerable conceptual complexity in the APIs that it makes possible. That complexity makes me personally inclined to avoid it and seek to rethink problems in a simpler way rather than add that complexity to the problem at hand.

All of which were reasons why I didn't mention it before...