the .45 gap is pointless. It's not the first short .45 to fit in a 9mm, and nobody remembers the last one either.
As for .357 sig, I have to disagree with the previous posters other than it is an accurate round. At 50 yards, you can tell it is flatter shooting than a .40, but it's not like the difference is really that meaningful.
It might depend on the gun, but I find it to be a harsh and flippy round on recoil. moreso than .40 IMO. Perceived recoil is a matter of opinion though. I might also be that I've only ever shot .357sig in a compact frame and am comparing it to .40 out of a compact frame.
.357 sig sucks if someone else isn't paying your ammo bill. It's pricey, and the necked cartridge makes it a real pain in the ass to reload. Factory ammo is really pricey as well.
IMO the real big loser issue for me is the noise. It's jsut too damn loud. A .357 sig with a 3" barrel is about the most irksome round i can think of other than something like .475 wildy (pistol round). Given the harsh recoil and flip, adding that noise to the equation makes it one of the rounds most likely to cause you to develop a flinch, especially for the recoil sensitive.
Might be cool in a subgun with an 8" or longer barrel.. except for maybe throat erosion.
I think by and large it is an invention trying to fix a people problem with gear.