Full Idea
If one confines one's sights to genuinely possible worlds, disavowing the impossible worlds, then metaphysical modality emerges as the limiting case - the 'unrestricted' modality that takes account of 'every' world - and S5 emerges as its proper logic.
Gist of Idea
Without impossible worlds, the unrestricted modality that is metaphysical has S5 logic
Source
Nathan Salmon (The Logic of What Might Have Been [1989], IV)
Book Reference
Salmon,Nathan: 'Metaphysics, Mathematics and Meaning' [OUP 2005], p.142
A Reaction
He observes that this makes metaphysical modality 'restricted' simply because you have restricted what 'all worlds' means. Could there be non-maximal worlds? Are logical and metaphysical modality coextensive? I think I like the S5 view.