...why? I mean, CT has a loot lockout restriction without the team restriction, which kind of proves how they could've done coil in a similar way. One thing I've always disagreed with is their method of getting people invested. To be honest, turns 1-5 never appealed to me specifically BECAUSE of this restriction, and now the latter turns are doing the same thing. By the time I was able to do coil freely I had already picked up full i90 gear and the appeal of running it had vanished.
More people might actually bother to do the coil of bahamut if this silly restriction was removed. There is quite literally no reason for it to exist other than to annoy players. If it's some strange method of 'gating' content, then it fails because you can still join higher turns as long as the party leader has been there already.