If you required every player to do the full Iksith quest line for yclist, spires, turuj, there would be a lot less people raiding those zones, and there would be a lot of people doing quests they dont enjoy at all just because its the only way they can continue to hang out with their guild.
Want to echo a sentiment in here kind of, from the dev side.
Having only one (1) guild do a zone for the first year or so of its existence sucked. They had a monopoly on feedback, so my sense of how anything and everything in the zone was was necessarily skewed. By the time anyone else got there I was tired of the zone and didn't remember how most of it was put together anymore anyway. The whole experience was kind of deflating: I didn't want to make content for just one guild. Even however many years later now (3?) not many people have seen the zone at all, maybe 3 guilds now? There are a lot of raiding players who'll probably never see it even as things are now. It has killed any interest I might have had in making any more really high-end content.
If I were to do what Nwaij was saying, I'd basically be saying: this content is so awesome and I like it so much that I want to make sure that the lowest possible number of players will ever get to see it, even less than now.
I'd rather just delete spires, honestly. I'd like more people to get to enjoy stuff I've put time into, if possible; not less. I use to be pretty well against ringers and all that, but you know: screw it. Having fun should outweigh rules lawyering. If you have to rules lawyer to deprive other people of fun just to protect your own fun, that's pretty dumb and the whole system should probably change. That inevitable sense of "it was set up in a retarded way when we did it, so it should be retarded for everyone forever" isn't very good either.
It's a fact that guilds are pretty fluid and can pop up and blink out of existence at pretty much any time and any tier. Trying to regulate things as if they weren't and as if every character progressed through each tier sequentially would be pretty silly. There's enough backgearing without enforced backflagging or whatever on top of it.
I think instancing would be worth considering if it comes to it. We have more than enough instance spots (currently devoted to almost-never-used-and-probably-no-more-than-2-at-any-one-time house zones) and our server can almost certainly handle it now. Competing might be fun to some degree, but I'm willing to bet that most of it is frustrating bullshit and that the un-fun of it outweighs the fun.