I've got to go with Pete K. on this one. In our current, cidr-ized world, it is simply not possible for an upstream provider to determine what is, or is not, a broadcast address in a downstream network. This is something that needs to be implemented from the edge in, not from the core out.
Don't forget that the original suggestion at the beginning of this thread was that UUnet should filter broadcast addresses on their Cisco routers because their Max TNT's couldn't do it, in other words take care of the networks on which the TNT's sit. It got escalated into a suggestion that they protect all their networks and all their customers networks in their core. Of course that's next to impossible! Point: Yes, people who have routers in their networks that can't be configured not to forward directed broadcasts should have this problem patched by filtering, (although it won't protect them from their own dialup users from being initiators) -Phil