I toured the USS Pampanito in SF once, that's about it. You don't need to be a submariner to know that it's capabilities are:
1) Undetected observation of enemy shipping and ports.
2) Stealthy interception and destruction of enemy naval power and shipping.
3) Detection and destruction of enemy anti-ship vessles
#1 will soon be replaced by the next generation of stealth tele-operated spyplanes.
#2 is already being obsoleted by modern missile technology, an obsoletion that will be accellerating over the coming decades.
#3 will be obsoleted by a combination of on-station ROV's and remotely fired anti-sub missiles.
The sub was a great ship, but like the battleship it is a tool designed to fight specific kinds of battles against specific enemy technologies. The realities of warfare are changing, and the attack sub will soon be obsoleted for everything but close-in shore defense.
I would think that endurance would be a problem for ROV's far into the future.