sink.arpa question

[jason at i6ix.com (Jason Bertoch)]

Ted Hardie wrote:
> Silly question: how well would using 1.0.0.257.in-addr.arpa match the
> need identified in draft-jabley-sink-arpa ?
> 
> It seems like it would be equally well guaranteed to be non-existant
> (short of change in the def of IPv4 and in-addr.arpa).  Like
> sink.arpa, it would get you a valid SOA and nothing else.
> 
> Am I missing something, or is this operationally equivalent?
> 
> regards,
> 
> Ted
> 

Isn't the fundamental problem that SMTP can fall back to an implicit MX? 
  None of these solutions will stop spammers from skipping MX records 
and using direct-to-host connections.  Shouldn't we just consider 
dropping the implicit MX back door as opposed to getting creative with 
MX records that spammers will surely note and avoid anyway?