Today, I was looking at diminishings of x3o4x3x, and suddenly realized that x3o4x3x is nothing other than x4x3x3x augmented with eight x4x3x||o4x3x's. Is this already known?
In any case, this means that x3o4x3x also admits a (probably maximal) metatridiminishing, another member of the 24-cell uniform metatridiminishings.