It would consist in 3 stages for inferno.
kill main bosses and find special key items to combine into something that sets off stage 2..
After you had made the item from stage 1 with the collection of items it turns all the champion packs into boss fights, consisting of one end act boss and lower bosses.
Example of pack, Diablo with skeleton king.
Once you get to the main bosses of the end of the acts diablo will be with them too.
For the diablo fight, diablo will not have any other bosses with him, instead he is like a uber hulk diablo.
You have to collect the items for stage3 by killing the new champion packs and all main bosses.
Strage. 3 Final Stage
You open a portal to a alternate reality where diablo and his minions have won.
You go to some sorta destroyed tristram where all 4 bosses are at. Where then you have to defeat all of them together in the same place.
Any way sorry for bad grammar/spelling mistakes.