EDIT: NEVERMIND. Thanks for those that answered, thought Duriel ,etc… was only available for Season 2.
I’m hoping this is discussed at their BlizzCon chat. I don’t see the purpose of going “oh you wanted extra bosses that should have been in at launch? Buddy… you only get to do that on OUR schedule.”
Absolutely
One more thing I’d like to have is a Vampire event where 5th round are 2 Bloodseekers in it 
All the bosses are already on eternal.
I’m not 100% sure, but I’m pretty sure all those bosses are live on the Eternal realm now.
Unless Blizzard goofed, the new bosses were added to the game as a whole, not just seasonal realms. They said as much in their announcements.
Who still plays eternal, at some point when the character slots are insufficient we may need to delete characters there, 2 free character slot ain’t cutting it if I’ll need stash mules.
Well hell I’m having the fun queued for game infinite server fun so I was just about to hop onto my Eternal characters to check, I only thought these bosses were in for Season 2. I might just have not kept up from the proper articles/news.