I think you should consider changing the nature of these areas, or scaling them down slightly to make them more accessible to the playerbase. I actually like the dragon lairs as designed, I think they are a tough and difficult challenge without being overly impossible, and having enough randomness that there is an ever-present element of danger. Similarly, hell does a really good job of creating the same effect although through different means.

However, I think that Tiamant himself is basically too tough. I like the idea of having an ultra-tough challenge, but having nobody able to do it in a year sort of suggests that the difficulty is too high, especially considering the ever-declining playerbase lately.

One thing that I don't like about it is that you only get one shot, so even if you were able to assemble a group that could take him down, once you failed the first time he is essentially undoable the second. I think you should take all the bonuses away from Tiamat for a failed attempt against him. Also, I think he is just slightly too strong in general. As you describe (I don't remember exactly your quote), you need 5 players minimum to take him down. Getting 5 competent players is very difficult, only having one opportunity to take him down is even more trying, and the fact that this assumes all the characters do what is optimal and have favorable synergy is a bit much, don't you think?

Also, I feel like only the first part of this will be responded to, but I'd like to bring up Hell too in it. It's a lot harder to do things in there now that there aren't groups of 10+ going down there all the time. I would guess that there has not been one item retrieved from 8th-9th in the last 6 years. I doubt those items will ever be gotten again unless a highly experienced group of vets consisting of characters designed specifically for Hell surfaces. I don't like the idea that you'd have to go to those lengths of OOC planning to possibly go there. Hell was designed with 100+ players online, not 40.

I like the idea of those Herald cabal powers to enhance exploration making a big difference in these parts. I REALLY like the idea of letting a Herald set a "waypoint" or campfire, a temporary altar, in an explore area, so that you will go there when you die instead of your pit as long as you are in the group when it is crated. I understand it's not really in the spirit of the whole place, but this would really give a chance for people to explore the area through attrition, and not discouraging people to not explore due to the time sink, the incredible cost of a mistake, and the fact that it is incredibly newbie unfriendly.

Also I was going to add something about ST, but I'll boil it down to this.

Some of the secrets, even though they are secrets, aren't worth very much individually. Some of them are worth a lot. Some of them have never been discovered. Many of the things will still kill you even if you know the general nature of what's coming because you aren't familiar with the area itself, or the various nuances. I just don't think the area is significantly diminished by the knowledge that is circulating out there. I would guess that me and Daevryn differ on that point. Anyways, I think it's certainly one of the most well written areas in the game, I think you should just put it back in instead of trying to preserve the mystique of it. I think it's more fun for you to watch players try your puzzles and for players to be challenged by your puzzles than to try to create a secret area in a game that just doesn't lend itself to secrets.

The other alternative is to just make it a brute force challenge. I don't really like that idea.