[ppml] PI policy discussion

[Tony Hain]

The primary objection to PI appears to be the presumption of long term
deaggregation. If the space used for PI assignments has structure it is
conceivable that service providers not directly involved at a level of the
structure could ignore the detail through aggregation. This requires a
little forethought in terms of laying out space. It doesn't require that we
do anything long term, it just creates the potential to mitigate the concern
about perpetual deaggregates.

Tony