Research is current. The military may well be using the technology already.
The reason these hearing enhancements seem so marginal is that the ear already does its job astonishingly well—so well that it's hard to imagine how to improve it. The normal human ear catches a gigantic range of frequencies. The frequencies that we do miss—at the very high and very low ends of the spectrum—don't contain much of interest anyway (unless you understand Whale). Our ears are already so acute that increasing their sensitivity may be impractical. If we picked up sound any better, we might be distracted by the sound of fluid moving within our inner ear.
So, we may be stuck with the ear we've got: With its dangling fleshy flaps, its dirt-collecting whorls and twists and sticky neon wax, it may look like a mistake. No one ever called the ear the window to the soul. But we're not going to do much better.