So, Blizzard had 2 goals:
1) let 90% of players to see all bosses in game
2) don't force hardcore players to leave the game
Imo, they could do it that way much better:
1) Replace some bosses in Naxx:
- Move Patchwerk to the end of Abomination wing
- Move Thaddius to Plague wing
2) Then make change to condition for gate opening to Sapph/KT:
- kill all bosses except last bosses in each wing
3) Include achievements to last bosses in each wing:
- Patchwerk enrages in 3 minutes
- Horsemen enrages in 15 sec after one of them dies
- Thaddius raid-wipe if someone touched another one with opposite charge
- Make some changes to Maexxna to make it harder
- Make big changes to Kel'Thuzad fight so it won't be a joke.
This way all casuals will still be able to SEE bosses, but won't be able to down them. And hardcore players will be able to minmax their raids, because they won't have gear from those 5 bosses at least + Blizz can make T7 tokens drop from those 5 bosses, so they won't even have T7 bonus so easy.
I think most boring thing of SWP and SSC/TK was that M'uru was single boss and wiping on single boss without other possibility is boring, and Kael'Thas was same single hard boss.