Possibly. The main problem would be keeping the price low enough. The flip side of that lack of familiarity is, I figure the target market for fantasy guns would be unwilling to spend more than $200-300. Not because those kind of people couldn't afford more, they just typically somehow have this idea in their head that you can get a full auto H&K rifle for $500.
So with that price range, you'd be limited to single shot break opens and possibly falling blocks, which take low pressure cartridges.
I figure that a company like that, the best bet would be to get as many movie licenses as possible to produce real firing prop replicas (there are a lot of people out there who'd kill for a firing replica of the Blade Runner "blaster," that one would be a gold mine). Licensed guns would be the bread and butter, with occasional limited runs of fantasy pieces just to keep things interesting.
But, there would also be the inevitable public/political outcry that fantasy guns are somehow "irresponsible." As if there's anything stopping someone from buying any other gun just because it "looks cool," or it was in some movie. We need laws that say that all guns should be ugly! Hot pink and day-glo orange! For the children!