Dunno if it really would be more expensive. I would guess the materials cost is about the same, and you'd reduce or skip completely the (probably significant) costs of polishing and bluing, which is both labor-intensive and has big hazardous waste management issues.
As far as demand, again, dunno. My observation is that SS handguns seem more popular than blued, although rifles seem to be less so -- although I think the market is moving in a SS/synthetic direction. Less maintenance, more durability, lighter weight...I do think that folks are right when they suggest that shotgun buyers just haven't sought SS shotguns, so unless the manufacturers find it worthwhile to try to steer the market that way, things are not likely to change (and I'm not suggesting that they should change! <g> ).