Since you ask, my thoughts are... I personally don't see why anyone would want it or want to pay the inflated cost of a designer round, with the .380 and 9mm available. But some like new things, good for them.
If you compare 30 SC FMJ to 380 or 40 FMJ from the same manufacturer the cost is about the same, about $.46/round. The problem is only ammo companies such as CCI, Hornady and Federal make 30 SC ammo and lower cost manufacturers like S&B and Magtech offer 380 and 40 for as low as $.36/round. Prices are based on what sgammo is asking for the ammo. Not many people consider 380, 40, 38 Special and all the other cartridges that cost about the same per round as designer rounds, unless they consider anything except 9mm a designer round.
The price of 9mm is much lower than any other centerfire cartridge. Which is one reason I shoot a lot of 9mm. But I do own and shoot other calibers despite the higher prices, just not in the same volume.
But more importantly I don't understand why Smith & Wesson is offering new firearms in a designer caliber, while not offering new products like the Shield Plus, or the M&P FPC in the proven and popular .40S&W. Makes no sense.
Its a lot easier to modify a gun to work with a less powerful cartridge than a more powerful one. Boutique ammo makers like Underwood offer 40 ammo that is is the same ballpark as a 357 Magnum when it comes to muzzle energy, nearly 600 ft-lbs (
40 S&W 155gr. eXtreme Terminal Performance (XTP(R)) Jacketed Hollow Point Hunting & Self Defense Ammo). If a Shield Plus chambered in 40 wouldn't handle it reliably the internet would be full of complaints about it not being able to handle "real" 40. Ammo from bigger companies isn't that strong but is still more powerful than 9mm by a big margin. That is probably why S&W only chambers larger, heavier guns in 40.
The original Shield was designed from the start to work with 40. I don't have one to measure but I bet if you weighed the slide of the original Shield it would significantly heavier than the one in the 9mm only Shield Plus.
I do think a FPC carbine in 40 would be interesting but since it is blowback it would need a heavier bolt and spring. For a lot of people the extra power would be worth the increase in weight.
Guns like the original Shield and Glock 43 have mostly been replaced with guns like the Shield Plus and P365 because they offer 3 to 4 more rounds. Companies like Magguts do nothing except sell products that allow an extra round or two. Somehow I never hear complaints about them trying to solve a non-existent problem. Running out of ammo could be a real problem.
The extra cost of of ammo compared to 9mm and small selection of both guns and ammo in 30 SC mean it will not be nearly as popular as 9mm but it does fill a useful niche for many people. The biggest threat to its future would be laws banning magazines that hold more than 10 rounds.