If the Joint Combat Pistol/Combat Pistol (CP) solicitation from 2006 is any indication it will have to be a production pistol. The military isn't interested in funding an R&D project.
The Glock 21SF wouldn't make the cut because they don't offer an external safety as the CP spec's require. Based on the pistols entered into the CP competition, my vote on the front runners would be the HK45, Sig P220 Combat, FNP45-USG, and the S&W M&P 45.
