Some options and methods about gear unlocking I've heard so far while shooting the shit with people; 

Separate it by tier
Separate it by stat value (hp/mana)
Separate it by boss
Separate it by whether it has dropped for us or not yet

An objection that seemed to continually come up when these suggestions are made, is 'but who will enforce this?'. 

I really honestly believe that most people are capable of following an honor system for any system we implement. Some few people may equip out of era stuff but it would impact raids much less than allowing it for everyone/having everyone do it, and you can rely on community enforcement [guildmates to tell officers about it], and maybe do a few random inspects to catch loose ends. 

Some people say but that is unfair, rulebreakers might get advantage other people don't have... that is true in real life too - lawbreakers get to do stuff law abiding citizens don't. It doesn't mean everyone is rushing out to break the law to get said advantages, or that the police are suddenly like okay this guy broke the law and we didn't catch him - have at it everybody! This is kind of an extreme example, but really any organization has rules and the majority of people follow them which is why rules work, despite rulebreakers. 

I totally think this guild is mature and trustworthy as a whole from what I've seen and I think the vision of having to go inspect everyone all the time and babysit gear is silly - most of the gear that is equipped out of era now is, as Nofia had said, 50hp/mana stuff, or Azaiel forgetting gloves for monk epic, or someone not knowing elemental BP couldn't be equipped... accidental or out of a lack of knowledge of where the gear is from.