That's a horrible cop-out. If the SPNKr had design flaws, it would have been replaced years ago. That's just how military procurement works. Good weapons stay in service until they are made obsolete by new technology or new tactics. Bad weapons are replaced by new designs before they can lose that new-gun smell.

Example: The M1 Garand was a good weapon for its time. It was a semi-auto rifle developed when everyone thought that straight-pull bolt-action rifles were the bee's knees. It had an en-bloc clip that could be loaded faster than stripper clips, but was vastly cheaper (Read: within America's production capacity) than detachable magazines. And it fired a bullet that was commonly available in a strained logistics system.

Advancing manufacturing technology and high production costs meant that the Garand was no longer a good weapon. It was a bad weapon by the 1950's, and was replaced by the M14. Service life: Twenty years.

Unfortunately, the M14 was a bad weapon for the intended role. Logistics no longer demanded that America's service rifle fire the common 7.62x51mm round, and that round was overkill at the ranges most gun battles were actually fought at. Worse, it was way too powerful to be controlled in full auto fire. Finally, the weight of the cartridge meant that soldiers could only carry enough for one firefight.

Therefore, the M14 was replaced by the M16 a mere five years into its service life. And for all it's faults, the M16 was a better weapon. The 5.56 is powerful enough at ranges of up to 300 yards, it is controllable in full automatic fire, and soldiers can carry more 5.56 ammunition than 7.62, weight for weight.

Once the M16's reliability issues were solved, the rifle was a great weapon. Other weapons may offer marginally better performance, but not nearly enough to justify replacement. Armorers are intimately familiar with it. America's logistics system is built to deliver the M16's ammo and magazines and spare parts. Any new weapon will have flaws in design and production that will take decades to solve; thus, the M16 won't be replaced until some radical shift in technology allows a much better gun. Same with the Kalashnikov, A-10 Thunderbolt, B-52, etc.

In short, if the SPNKr has lasted through twenty five years of war and an additional eight years of peacetime, Then it's not going to be replaced by a design that offers the same damn performance.