Hmm.... Box Rule, SMOD, MMOD. Not sure if there is such a thing as MMOD, but it seems to be the direction espoused by Franck.

Regardless, strict OD classes tend to be a price/technology/design snapshot in time. As these things (especially strength of materials) improve and move on, the class risks becoming out of touch and withering away.

I think a merit of the box rule is it allows more flexibility to adapt and stay relevant. However, the box also puts limits in place to prevent the class from becoming one where the biggest pocketbook wins.