The reason this subgroup taxon does not exist is because there is not a documented need for it.
Soil Taxonomy has eight attributes which are defined in chapter 2 of the second edition (1999). The third attribute of the system states that the taxa represent real bodies of soil that are known to occupy geographic areas. The system does not try to anticipate all possible taxa that MIGHT exist.
The great group of Haploxerepts currently contains two subgroups using the adjective