Policy Statement on Address Space Allocations

Option 5: Provider X can announce nothing outside the area, except
to people who are paying X for transit to all X-reachable sites
and networks.

This would work great if all the backbones touch down in the area.
Customers out in the Rest of the World get transit through their
backbone to all the area sites. Other regional networks or areas
get transit to it via whomever they get global transit from.

Which works fine as long as only one area on the planet ever implements
Option 5. Any pair of such areas without internal connectivity won't
be able to talk.
Seems like a scaling problem.

No, they can talk just fine. In the worst case with asymetric paths,
but they can talk fine.

Backbones A and B, small providers a in region 1 and z in region 2.
a buys transit to the world from A and is in the region 1 block.
z buys transit to the world from B ans is in the region 2 block.

a->z goes a->A. A knows about region 2 block, sends it to region 2.
Once it reaches there, it either goes A->B->z or A->z if there is a
direct interconnect somewhere. z->a goes out the z->B pipe, and
thence to region 1 and either B->A->a or B->a if there is a direct
interconnection somewhere.