Air-independent propulsion technology does sound pretty interesting, as oxyegen is the number one limiting factor on how long a diesel-fueled submarine can stay submerged. The trick is to not only make the fuel combust without using up the oxyegen supply that the crew itself is quickly burning through, but to do so more cheaply than it would cost to just go nuclear.

I seriously doubt they'll ever match the six-month periods nuclear submarines can attain, as the simple fact that nuclear fuel doesn't consume any sort of material crewmen need to survive ensures that any oxyegen-conserving technology that helps diesel subs stay under longer will help nuclear subs even more.