/19 addresses and redundancy

Since you would need some type of settlement system in order for
this to work, if you could get a third party to maintain the access
lists information, and manage the settlements, then you might have something.
I.e. a third part, Neutral Settlement Authority (NSA), uses a database
such as the IRR to maintain a set of policy statements, that are readable
by the rest of the Internet, They convince a few providers, say
Sprint and Digex, to listen to them for prefix length filter exceptions,
in return this Neutral Settlement Agency, pays these providers for this
service. The Neutral Settlement Agency then, posts to Nanog, or
other lists, saying it will cost you X dollars to have your execption listed
with us at some cost of what the costs to providers A and B are paid plus
some percentage for profit.

Looking at this, pretty much any BGP speaking peer at the MAE could do
it with the correct configurations, and the RA service could do it also,
although there are those that won't touch an RS with a 10 AS BGP path
extension, although perhaps if they were getting paid for it...

The biggest problem I see with prefix charging is the many to many
contract nature, which is where a MLPA type situtation is helpful,
but must be setup so that different providers can negotiate different
rates, as network sizes differ, and the cost to carry those prefixes
internally varies.