When the gun that we now know as the Springfield EMP was first announced, it was called the Defender, and was chambered in .45 GAP. I thought it was a pretty cool idea, shrinking the 1911 envelope around a shorter cartridge. If that gun had come to market, I might be a huge fan of the GAP round.
I just don't like the various "platforms" that support the cartridge today. If I wanted a Glock, I wouldn't buy one chambered in an oddball cartridge like the GAP.