The reason why it needs to be changed in my opinion
1. we now have seven stages of fear instead of 3 or really 2 since shaken may be a fear effect but things besides fear cause it in the core rules.
2. It has never made any sense that a character that is above level 9 would not be afraid of something like Cuthulu since it cannot affect anything above 9 hit dice at all as a base rule.
3. the new fear system does away with fear immunity telling you to downgrade the penalties by 2 levels not due away with it entirely which makes sense someone might be able to act even though they are terrified of something else but only a fool is competently immune to fear.
4. almost no creature in the bestiary's that has frightful presence is something you would throw at a party below level 9 anyway making the frightful presence aura at base pointless as written from the core rules.
5. Several fear effects in the game should take advantage of the new 7 stage fear system for the same reasons as frightful presence needs to be changed. If you cast a level 1 spell like Cause Fear which causes fear a character should not be immune to it with a 7 stage system just because they have 6 HD or more they should downgrade the effect with a 7 stage fear system it just makes more sense if nothing is immune to fear anymore and instead just downgrades it. The spell might still cause them to be spooked above a certain number of hit dice but it should still have some level of effect no matter how many hit dice the player character has if they fail their save.
Its like Paizo did not think through the rules changes or how it would be different with a 7 stage fear system that is what I am saying. Just because your character is a level 14 bad ass when a CR 25 ancient wyrm lands in front of you its frightful presence should still work to some degree maybe not enough to make you poo your pants and cower in fear but still affect you somehow. Otherwise what is the point of the aura; Also no matter what if a 150 ft. long dragon lands in front of you as a human being you are going to have some reaction just based on how big it is after all the entire party could fit in its mouth.