I concur with the comments raised so far. I think it would be great to do a better job of outlining the problems with essential packages in debian-policy. I don't understand why we would tie our hands though. A consensus of debian-devel seems adequate to consider those issues and evaluate them. If after making that consideration we decide to create a new essential package, we're going to do that policy not withstanding.
I would support a statement in policy that as of the time of writing we do not anticipate ever creating a new essential package. That would help people considering proposing making an essential package know they are probably looking at things the wrong way. --Sam