.357Sig has some of the negative marks of .357 Mag but without the versatility. The worst aspects are the harsh report and tendency to perform well only in a very narrow weight range (basically stick to 125 gr).
I like the concept, but I don't think it will ever be highly popular. Having said that, I love oddball calibers.
As long as there is enough of a following to have premium ammo and supplies available, and of course guns to shoot it, it will survive. I don't think it will ever be a museum type curiosity the way .45 GAP and .327 Mag eventually will.
Mauser Werke, Schmidt-Rubin, Remington, Colt, H&K, Weatherby, Browning, Ruger, Savage, Marlin, Mossberg, Saiga, S&W, Sig Sauer....a few friends of mine