One compromise might be for the provider to reserve a block which can
> re-used by more than one customer, but that block will still consume a
> chunk of the provider's space.
Don't you think that this would be asking for trouble in the event
that the customer does eventually connect? It would be best
to have the customer with a "legal" network from the start.
No, since the customers in question have explicitly stated that the network
numbers will be used for their private networks, which will, for policy
reasons, not be reachable from the Internet. They would use the new network
numbers with the explicit caveat that IP addresses assigned from them would
NEVER be routed to the Internet, so they would have to re-configure any such
hosts if they later needed Internet access.
The issue here is how should we deal with private networks which run TCP/IP
but which are not intended to be part of the global Internet address space.
Given the very finite size of the IPv4 address space, it is silly to assign
network numbers to systems which are never intended to be a part of the global
Internet. This issue was first raised long ago, but recent growth of the
Internet has made it more important that we come up with a policy for dealing
with unconnected networks.