[SpamCop-List] C/R systems

[Spamcop]

I read in RISKS today that Earthlink has implemented a customer option for
Challenge/Response to Emails, why does nobody think of a more selective C/R?

For example select  blocklists and only apply C/R to selected mails flagged
by certain blocklists? Presumably if intelligently done this could occur
during the SMTP Envelope transaction so that the bounce mail would contain
the C/R, and innocents wouldn't be plagued by needless C/R mails.

I'd love to C/R any mails out of spamcast space with a web site that says
Yout ISP so-and-sosends too much spam so do whatever to communicate with me.

Other mail I'd love to simply have rejected out of hand, ie mails from
SPAMHAUS,  open relay/proxy or SC BLs.

then C/R mails that get through the first from, say, SPEWS listed sources

This would eliminate a lot of the harm from C/R systems.

Any one seen such an implementation?

Berny