Right up there with the .41 magnum. Great round, tough to get, expensive if found, and for those that reload, it can work great.
The GAP and 10mm are a good round, it comes down to "marketability".
Sonny Crockett had the Bren Ten, and tried back in the eighties,...(realistically it was out there in the real gun world to rival the super dee duper LEO rd., which was the 9mm. back in the 80's).
It developed a following, just like the .45GAP, but never hit the mainstream like the .40 S&W. The 9mm is here to stay, the .45ACP will never go away, and the great rds. that they are, .41, GAP, 10mm, even to an extent the .32 Magnum, in the Rugers.
They are fine rds. but may be impossible to get if the SHTF.
So either stock up, reload your own, or stick to a caliber that will be "less" harder to get or be bartered for.
Just like 7.62X39, it will always be around "somewhere".. 10mm, and GAP, I doubt it.