Modal realism is the belief that all possible worlds actually exist. Actualism is the belief that possible worlds don’t exist at all. What are some examples of modal-metaphysical views which try to walk the line between these two extremes - that is, give possible worlds some status as existents that is different from the actual world?
Incidentally David Lewis already philosophized your speculated middle position which is called ersatz modal realism defining possible worlds as merely "ways how things could have been" and relying for its premises and inferences on assumptions from natural language according to reference here and here:
Lewis looks at the alternatives to his kind of modal realism. He takes himself to have established that we need to have possible worlds of some kind in our ontology, but not that these possible worlds must be concrete. In particular, they can be abstract, or what he calls “ersatz” possible worlds.
Ersatz possible worlds can be understood as maximal states of affairs; maximal properties; recombinations of actual bits of reality; as maps; or as entities built from propositions or sentences. The question was: can these approaches be extended to include impossible worlds? The states of affairs approach can, with some modification, accommodate impossible worlds. The property approach too can, with some modification, be extended to impossible worlds. It is argued that the extended approach is best viewed as a form of linguistic ersatzism.
So ersatz modal realism is a kind of maximalism and Lewis argued against this position. For example for linguistic ersatzism, if you just use maximal sets of consistent propositional sentences as abstract objects replacement for possible worlds, these sentences are nothing but representations which are not ontic concrete objects themselves. As representations they must be further derived by some distinct ontic object in our actual world, but then how can you make sure your imagined maximal sets of consistent propositions will exhaustively contain all representations there are? Maybe tomorrow some aliens are suddenly known in our actual world but your original sets excluded this case before the phenomena of an entirely new category become known! By contrast, in modal realism all possible worlds are ontic and thus cannot be exhaustively defined by some representational set of sentences...