After 1500+ cave divers I really believe in this, matter of fact in a new system I become the intro diver and dive to 1/6s, and then build on learning,because you must always remember- line doesn't guarantee an exit, just increases your probability of survival.
nothing guarantees exit and I TOTALLY agree on progressive exploration... so if historically 3rds was the rule...for EVERYONE... why not make a push to bring it back and then leave it with the diver (which its open now anyway, breaking 6ths is a choice) to dive to what ever level of gas usage they feel appropriate for where they are diving.