I don't understand why you suggest creating a debtags facet replacing sections, except if you plan to give exclusive control on it to the archive maintenance team as opposed to the rest of the tags. Most sections seem to have already a corresponding tag (but it would be good to check that all useful sections have a corresponding tag if that was not done already).IMO, it would make sense to merge Debian sections into a debtags facet so that you can have multiple sections when it makes sense. The facet could still be controlled by ftpmasters if that was desired.
And aptitude could use that facet to keep a logical tree but a package could then appear in multiple sections. Cheers, -- Raphaël Hertzog