The real challenge isn't going to be beating Ifrit (extreme). They'll probably make his moves more unforgivable, give him more HP/resistance/etc... but with enough time/skill, any experienced group will take him down (assuming, of course, that they didn't change the fight mechanics entirely... I'm a bit worried about the lag and animation lock, though).

The real challenge is going to be finding seven other people that are at that point in their relic quest that are also skilled enough to pull it off.