Terrible, terrible, terrible idea.
Gear locked content is a terrible idea under a lot of sides.
This game is new and has already an insane elitism on it. SE, don't worsen things.
This is one of the things that makes me think about unsubscribing. It creates a really unhealthy and unfriendly community.
And this comes from a player who loves to equip his character to the max, in every MMO.
I agree that finding undergeared people in a Garuda fight may be annoying, but if I use the duty finder I accept that I may find such groups. In that case, I can choose to leave, a 15 minutes debuff is not such a big deal.
If I'm not ok with that, I'll simply put up my group and not use the duty finder.
