I too think that a cheap (say $150-250) American-made defense/ service revolver would sell well. Think a self-defense oriented Heritage Rough Rider or a modern version of the Iver Johnsons that people bought for years. This market was serviced by police surplus K-frames for years but those are drying up.
Why? I think a lot of people gravitate toward revolvers for home defense due to the inherit reliability and simple manual of arms. My dad, for instance, isn't a big handgun guy, and he's perfectly happy with my old, Australian-surplus Model 10 that's basically on permanent loan to him. Load it and forget until you need it--I know, not the philosophy anybody SHOULD have, but the philosophy a lot of people DO have.
I'm aware of the Armscor revolvers that are out there--they're around $240 and seem roughly but well built. I've thought of picking one up as a front-hallway gun. But around here I've only ever seen a few at gun shows, whereas every gun shop seems to have a few Heritages. Maybe Heritage should just make K frame clones and sell them for $200. I'd buy two.
Plot twist: I think what I'm describing would sell even better if you chambered it in 9mm and designed the chambers such that you didn't need moon clips.
Edit: I also think a .410/ .45 Howdah/ Auto-Burglar pistol would sell well if it was priced reasonably and by "reasonably" I mean no more than $150. I'm aware of some of the .410 double-barreled derringers but my impression is that these were pot-metal POSs. I don't think it would be that had to make these cheaply--just overbuild it out of steel and wood. Don't ask me why, but people do seem to like their Judges and Governors just fine. If I could get one for $150 I might do it and carry it when I'm out walking for snake/ dog/ zombie squirrel deterrence.