>>>>> On Sun, 11 May 2014, Samuli Suominen wrote:

> For reference, a mail from the amd64@ lead KingTaco from 2007 at
> gentoo-core@:

> [...]

> If you are the maintainer of a package that currently has open bugs
> for amd64 stabilization and own amd64 hardware, please do your own
> testing and keyword your packages.

Really, an e-mail to -core from 2007 is a great reference for a
policy. ;-)

So, could this sentence be added to some document where it can
actually be found? I'd suggest the devmanual:
http://devmanual.gentoo.org/ebuild-writing/ebuild-maintenance/index.html#stabilization-rules

Ulrich