They covered the major concepts. The other concepts can either make do until the rest of the subclasses get printed, or you can port them over with relative ease.
I mean, we are in theory "missing" knowledge, nature and storm. Two of which are easily (and in my opinion better) handled by the Druid and the last one can be Trickery or light domain easily in a thematic concept. The Light actually fits really well thematically with Knowledge, since it is about "knowing things" and "Revealing the truth".
Plus, ALL the classes could have more concepts mechanically supported. That's why they all have more subclasses than these four.