Not each threshold as there would only be one which cameras would either pass or not i.e. capable of publishable quality(CPQ). The variable would be the maximum size at which CPQ still holds true. So, if applied presently, the larger format Nikons and Canons would still come off best, as indeed they should. But for example, instead of the Samsung GX20 scoring 85%, it might be given a rating of CPQ/A3. In other words, capable of publishable quality up to A3. This is a much clearer and more meaningful indicator of its ability for the buyer than 85%, which implies it's a lesser tool than all those scoring above it. The narrative of the review would be the place to discuss any particular strengths or weaknesses.

As for who decides, being in the business as it were, magazines and/or their reviewers are well placed to recognise publishable quality or otherwise. I don't think I'd have too much trouble agreeing with them.

If something is incapable of publishable quality at any size, like my camera phone for example, then it is a consumer snapper/toy/novelty with poor image quality. It would be good to know that too.