I was eventually planning to turn it into the cosmology of the inner planes. The elements are supposed to be the building blocks of all creation in D&D, except for magic, which was a major driving factor in my choices. And yes, I was hoping to turn many things common in D&D, like energy types, into actual elements, hence why Force and Sound are on the list. As for the quasi-elements, I felt that several of them should be on the list (Wood, Force, Poison, etc), but were too numerous to all fit in the para-elements. Many other quasi-elements were thought up as space-fillers because I could not figure out something better to take that location, and ended up on there to flesh out the table (Meteor, Moon, Cloud). Also, I tried to pay homage to the older editions, and included all of the previous para- and quasi-elements from those, though some ended up in new placements (not that they hadn't already been re-arranged a few times).
Using them for tags is a good idea, especially since many already exist as such. Plus, extra clerical domains could easily be fashioned around them.