While I do like some of the points, I am not so sure about the frenzied parts. If it was tuned properly, you wouldn't require a health stoppage. You would either increase total HP or mob defense. Having damage stop doesn't sound very effective for being efficient. You could build in phases to increase the difficulty and have the boss utilize Random AoE's like the boss in a dungeon that I forgot the name to already. The one where it is just a bunch of random red circles that show up at random requiring some dodging. But then again we know about them red circles... I think it was darkhold. The other thing is that by limiting FATE access to a set number of people, you will have campers and griefers waiting to pounce on them. Essentially, it would just be a more frustrating race to the FATES hoping to gain access. Since we already know there are teleport hacks going around, it would just be a huge source of contention and more work for SE when they really have a couple more pressing issues right now, such as getting things stable in general.

With all that said, I would like to see many of your ideas implemented over time. The only lore that goes with a lot of Fates is the three or four sentence paragraph under the FATE name. Could be much more involved than a running party across a map.