I will fully admit that I am a person to accept major change slowly. That said, if I am to be convinced to change (and I have been at times for good reasons) there had better be a legitimate and very good reason to do so.
I am bewildered by people who buy guns chambered for ammunition that does nothing any better than what is currently available in other very close to spec. cartridges. I am also dazzled why someone would buy a new caliber that is going to be scarce, hard to find in any meaningful choices and expensive at best.
Now don't get me wrong here, if something comes out that is revolutionary, does perform much better than another close in caliber cartridge or has a special purpose that you are looking for - go for it! Just be prepared to buy a lifetime supply of ammo, reloading dies and components to feed it because new cartridges seldom enjoy a long life.
Now let's mention the guns themselves.... If a new cartridge is developed and it turns out to be a bust or unpopular down the road, where does that leave you? Are you going to be able to sell it easily and for a good price or are people going to shy away because of unavailable reasonably priced ammo? Are you going to be able to practically buy components and reload ammo for it? Do you have the time and patience to reload? Are you going to actually spend lots of hard earned money to buy enough ammo to feed and practice with it? And most of all, what are you really accomplishing with that newly invented gun/caliber combo?
Make no mistake about it - many new fangled cartridges are "invented" to sell more product, market to different people and sell more guns and ammo. I understand that is the American way, it is not a new concept and will aways continue. Yes, there are on rare occasion in the gun times when ammo company's or firearms manufacturers do come out with new and viable products that do change things drastically and make a huge practical advantage. One such invention would be the relatively new crop of Micro 9's that came onto the market over the last decade. Another would be the invention of Kydex holsters, although I do not personally like or own any of them - I can see the reasons some people do.
So all I am trying to convey here is that before actually buying a "new" caliber firearm, think long & hard about the ammo supply, availability and what that new caliber is really going to do appreciably better than what has been a time proven, loaded for a readily available cartridge for many decades.
The reason the 9mm has been around for over 100 years and is now more popular than ever is simply because it is about the best cartridge there has ever been in a small, relatively lightweight weight convenient package. As much as the industry has tried, I am unaware of any other cartridge that is similar in size, weight, velocities and power that will outperform today's 9mm ammo and firearms chambered for it. When it comes to price and availability nothing else comes even close!