[ppml] 240/4

I just heard a part of Paul's comment about 240/4, and it sounded like Scott
commented about implementations being difficult to fix.

Even if the vendors implemented a change and shipped it within 18 months (an
aggressive window), there is a very, very, very large installed base of
systems that can't/won't be upgraded to allow use of a block that was
'undefined' at the time they were tested & shipped. By the time those work
their way out of the network, we will be long past the point where the 240/4
block might have been useful.

Tony