Most new calibers in what I'd classify as "in-between calibers" usually fail or become really unpopular, very expensive and hard to get. I usually say, "stay away"! I would also (for the most part) say the ammo company's and firearms manufacturer do this for only one reason - A MONEY GRAB!
Buying a firearm in one of these odd-ball calibers would require hand loading or going forward a large bank account to acquire ammo. My opinion would be to stay with long time proven popular calibers like the .22LR 9mm, .38 spl, .45 acp. Secondary calibers that are somewhat popular and still readily available are .380 acp, .40 S&W, .357 Magnum, .44 Magnum. Calibers I'd shy away from are .41 Magnum, 357 Sig, .30 carry, .25 acp, .32 acp & 10mm. Any really exotic calibers such as .357 Maximum, 30 Luger, etc are basically now for collectors only.
I used to LMAO when one of my Pheasant Hunting Bud's would have to replenish his 16 gauge shot shell stash. Most big box stores do not even carry it anymore and the smaller LGS's that do, charge an arm and a leg and only ave limited choices in shot size and brass heights.