I'd argue ITA Matrix serves folks that know airports and aircraft well enough to figure the human factors in their heads (e.g. if you can fly Delta and connect

I'd argue ITA Matrix serves folks that know airports and aircraft well enough to figure the human factors in their heads (e.g. if you can fly Delta and connect in either AMS or CDG, choose AMS), and just want to find a valid solution set at the lowest price for a query. The lack of split ticketing means you will be protected in the case of a misconnect. I'd say this is a good case for a declarative language like SQL or Prolog: "just give me X that satisfies Y and Z, I don't care how you get it." Existing search engines either have a painful number of dropdown menus or are free-text only with limited power user features.