When Blizzard announced their proposed schedule for the Sepulcher of the First Ones raid, they added a twist that they hadn't tried before in the modern era of World of Warcraft; they split up the raid so that not all bosses would be available on week one of heroic. This was something that they hadn't tried before in the modern era of World of Warcraft. This was done for on-theme lore reasons related to the "cryptic" nature of the patch, and it served the purpose of elevating the status of those last three heroic bosses by separating them from the other heroic bosses.
The Reaction of the Community
After seeing this decision, many members of the community praised the concept of using a TBC to "spice things up" in a tier by introducing a novel twist to an existing element of the game. This, in turn, gave rise to the idea that Blizzard should double down and prevent these three bosses from being tested on the Public Test Realm as well, in order to further increase the level of difficulty they present to players. In the end, Blizzard decided to go with this concept, and as a result, we got a launch of the Sepulcher with three bosses that hadn't been tested and wouldn't be seen until the week of Mythic.
The effects of the staggered release of content
This decision had a great many unintended repercussions as a result of the fact that the tier featured an innovative new feature. The effect that it had on the process of acquiring tiers was by far the most significant consequence of delaying the launch of these three bosses. The fact that these bosses couldn't be fought on any of the four difficulties until the mythic week, and that they each possessed two of the five tier pieces, meant that there was no way for players to acquire a four-piece tier set until at least the second week of the event.
Earth - DK said:
I think it would be better if they did staggered releases with more weight behind them
For example, they could release bosses 1-8 as a single raid, and then a few months later they could do a very difficult three-boss raid
If they are not going to do that, then this method is extremely frustrating because it prevented players from obtaining 2/5 of the tier's pieces for the first week, making people's lives more difficult through random chance
Even more significantly, this meant that there would be one fewer reset necessary to accumulate these slots in order to enable trading on easier difficulties
Due to the nature of cascading loot trading, this "lost" reset meant that characters who wanted to complete a 4-set on the first week of mythic were required to loot one of the tier items off of Lords of Dread or Rygelon
This meant that characters who wanted to complete a 4-set on the second week of mythic were required to loot one of the tier items off of Rygelon
This, in turn, led to the creation of a bottleneck for raiders who wished to compete in the Race to World First. This bottleneck was analogous to the one that was introduced by the Shards of Domination system in patch 9.1, in which the completion of a shard set determined whether or not a character could be used for progression. Because completing a four-set was one of the single most significant ways to increase character power, and because there was only one week to loot these items, it meant that their loot was the single most important factor in gearing for the entirety of the race.
Last but not least, one significant consequence of delaying the release of these three bosses was that, by the time they were made available to the general public, other bosses already possessed higher item levels. The fact that the early mythic bosses dropped item levels of 278 and these three bosses dropped item levels of 272 meant that the only reason WOW gold classic made sense to do them was to acquire tier sets. Unfortunately, as a result of this, very few guilds even attempted to kill The Jailer on Heroic difficulty until they were exceptionally deep into the tier. This was done in order to avoid wasting any time on a boss that didn't have much in the way of rewards, and it resulted in very few people actually killing The Jailer on Heroic difficulty. There are currently more guilds that have taken down 4/11 Mythic Bosses than there are guilds that have taken down the Heroic Jailer.
The Effects of Disguising the Bosses
Putting aside the acquisition of loot, there was another interesting effect that hiding these three bosses from the player base had on the raid as a whole. Preparation and planning were, at best, speculative. Specifically, the loot was hidden from the players. Because the only source of information about these three bosses was the dungeon journal, it was extremely difficult to devise comprehensive strategies, compositions, and even WeakAuras for taking down these bosses, who were guaranteed to present a significant challenge.
It also meant that if Blizzard made any mistakes in tuning or bug testing, these bosses could become extremely challenging or even impossible to defeat. This was a very real possibility. Because there was no player testing on the public test realm, the testing for these bosses had to be done in-house by the Blizzard testing team. This was done to ensure that there were no major bugs when these bosses were released to live servers. Thankfully, they did an outstanding job, and there were very few bugs that had a significant impact (we'll just ignore the Jailer's shield on mythic for the purpose of this discussion).