Hello Chris,
well yes, I have seen them already, but the security of user-contributed AMIs" warning plus the
"This is a RightScale Open Source MultiCloud Image supported by the
community only and is an alpha release not recommended for production
systems." note regarding Rightscale AMIs specifically make people anxious.
So I would normally expect from Debian to publish officially S3 backed AMIs for squeeze at least, and for wheezy maybe it would be enough to publish S3 backed AMIs like the way EBS backed wheezy AMIs have been published so far (as a cooperation between Debian, James Bromberger and Anders Ingemann as I can understand so far).
Best regards,