I think these suggestions of adding units like l/d, ml/d and the more generic VOLUME/TIME, as well as adding the data type DV_INTERVAL<DV_QUANTITY> are reasonable additions.
I’m wondering whether mass/time would be more of a dose formula rather than an administration rate? Do we have practical examples of medications that are actually administered at a “rate” and whose administered form is measured as mass and not volume?
Tbh I’m not entirely sure whether changing the order of units would be a breaking change. I would suspect not, since actual persisted data only contains the UCUM unit symbol, and not the numerical order from the archetype.