filtering long prefixes

Are you suggesting some sort of exchange point or NAP specifically to
break out longer prefixes from shorter prefixes that cannot be
topologically aggregated? Would something like this enable people
to maintain provider independent addressing (i.e. no renumbering) by
merely paying a fee to an exchange point that is well connected and
settling for less optimal routing?

If this will work in practice, it seems like the perfect tradeoff. On the
one hand you must renumber when changing providers but you get optimal
routing. On the other hand, you avoid renumbering but you pay a few bucks
and have less than optimal routing.

Am I missing anything here?

  Perhaps a couple of things:
    - Common transit agreements for all particpants
    - Single point of attachment, ie you must renumber
      if you home to another provider or exchange.