From a global point of view, it may be a success. I say this because there are many foreign countries that prohibit their citizens from owning firearms that are chambered in military calibers.
The .45 GAP would not be prohibited in these countries like the .45 ACP happens to be.
As far as the U.S. of A. goes, too soon too tell. It all depends on how well the gun writers embrace the cartridge and if they all write glowing articles about it.
Mr. Gaston Glock certainly is no idiot, so if he thought it worthy of research, design and production, that is probably a good clue that it will be a success.