This seems brain dead. I think the intent of 1597 was to say here
are some numbers you can go play with privately. Since they are
private they should never appear on the public Internet, anywhere,
Actually, the conclusion that I would draw from this (and that others
have certainly drawn) is that RFC 1597 is brain dead. I'd certainly
recommend that anyone who was contemplating numbering their network
*not* use one of the 1597 numbers, and if their network provider tries
to force them to do this "in order to save address space", to go find
another network provider.
As you've pointed out, by using the 1597 numbers, you're guaranteeing
that that you can never use those numbers on the public Internet, and
you'll never be able to use more than one network provider. Even if
most of a companies hosts are behind a firewall, they'd still be better
off using globally unique numbers.
After all, if we all do our jobs right, maybe someday we can make the
firewalls go away....