Why not have more GT instances to accommodate more time zones?
I think the current system is actually restrictive for those who actually play, and have a guild with friends for fun in comparison to 'farming' guilds (aka ghost guilds) which are most likely owned by someone with multiple high levels and can plvl themselves. No matter what level restrictions you give them, it will not benefit the actual player base trying to have fun opposed to those who can invest more time and money.
I've met many 'newbies' or people who just came back from a break who are stuck around level 70-90. These are people who are active, but can't join GT (unless they join an established guild which meet the requirements).
With more slots, even if we can't eliminate those ghost guilds, more actual, active guilds will be able to join, not to mention the time zones. You could have two instances of GT a week so you cover 2 time zones instead of 1.
There are ways to restrict people from participating, for example, having different rankings of GT:
-> Beginner match for guilds who have never done GT before, also checks that the guild members have not done GT before. This should have lower rewards (and I'll like to see someone crazy enough to go levelling new characters every single week)
-> Novice GT, which checks that at least 8 (or more) members of your guild (from different accounts) have been active in the past week. Active as in every second day you're not only doing 30mins of attendance. Perhaps a culminative of 1 hour per day or 5 hours per week.
-> Expert GT, for members who are capped: Guilds with at least 8 level 135s (from different accounts), who have been active in the past week
You could also have a guild points collection system, so that guild members log in and complete specific but simple like guild dungeon runs (or just count the dailies you all do dailies anyway), and the guilds with the highest amount of points per week can get in.
This would be a hidden ranking, no one will see it until the results are tallied and guilds appear on the GT list. If they can count how many quests everyone's doing for the Gamigo 2020 I don't see why they can't count a guild's member daily quest count. Also the count stays in the guild, so if a member leaves, the count still stays.