I think it's a bit premature to abolish source routing. Source
routing might become a valuable tool in a future fragmented DNS.
you're a little late. source routing was effectively abolished
when RFC 1123 was published...at least, hosts were not required
to honor it then.
frankly, it would be really insane to re-establish source routing
for email in order to make it easier to fragment DNS. if we're
going to take two giant steps backward in networking, why not go
all the way back to semaphores and smoke signals?
Keith