I think there are niche markets and the key is the size of the niche.
- Quasi-full size single stack 9mm. Slim is easier to conceal than fat. Barrel length is largely immaterial. 5" gets more difficult, 4" - 4 1/4" is the sweet spot. Less than 4" is easy to conceal, but now you're out of the "full-size" category. The cross-over for this niche is the people with smaller hands who can't handle the girth of a double stack. Let's look at mainstream market. It's fine to say that guns should be comforting, not comfortable, and a double-stack nine with 15-17 rd capacity is what you should carry and if it doesn't fit your hand or clothing well, suck it up and change. That works for a top tier and is legitimately good advice. But if you are a gun company in the business of making, marketing and selling guns, you look beyond that top tier.
I work part-time at a gun store because I like it. I like being around guns, handling them, seeing the new stuff and helping people, most of them first time buyers, select a gun that fits their needs. Most new shooters are looking for a gun for home defense. Many of them say that they are also considering or going to get their concealed carry permit. Almost all are looking for something that fits both needs, which is tough to do. If I had a slim, full size 9mm with a 9-10rd capacity, that fit their hands, had a reasonable sight radius and less recoil than the small 9's, they'd be very happy.
There is one small, sub-niche in this category that by default, gets shunted to revolvers. Those people who can't effectively run a slide (most of the time). In most cases, they don't have the grip strength due to age or nerve impairment. Beretta used to make a number of guns, from .22LR to .380 with tip up barrels. That allowed the user to tip up the barrel, load a round, and have a full magazine without having to run the slide. What do they do if they have a malfunction? Again, let's be realistic. We tell these people they need to practice and train and 95% of them won't do it. Even if they had the grip strength, under stress and fear they aren't going to remember how to clear a malfunction.
- 3" - 4" medium frame revolvers. I talked about the revolver crowd. Revolvers are a default option for those without the grip strength for a semi-auto, or don't want to deal with the complexity of loading a magazine chambering a round, safeties, decockers, unloading, etc. Open a cylinder and put in ammo or remove it as desired. We know the issues with an airweight, 5-shot J-frame. For this crowd, a 6-shot K frame makes more sense. 3" - 4" barrel. .38spl, though marketing would probably prefer .357. And this is my preference, a hammerless (shrouded), DA design like an upsized 642 or the new Kimber. Give it a good DA trigger pull. No safety, no locks, no exposed hammer to snag or tempt them to thumb cock it. And...an aluminum frame. Keeps the weight down without greatly increasing recoil. Round butt with comfortable grips that don't leave the little finger hanging. If it was priced between $400 and $500, I'd sell a shit load.