Yes, in some sense it's an obvious default, which seems to go largely unrecognized (even by those who understand thermodynamics), maybe due to a bias towards thinking that value scales linearly with material. But I don't want to claim too much. There are a number of caveats I didn't mention in my post:

• Some space-time geometries may have better entropy dumps than black holes. In an open universe without dark energy, for example, the cosmological background temperature goes to 0 and negentropy is essentially infinite.
• Why make negentropy the object of fair division, instead of value created from using up negentropy, which might not be a linear function of it?
• Why should individuals own matter? If they don't, then our intuition about what constitutes fair division would change drastically.