Blizzard Entertainment announced the Diablo III: Rise of the Necromancer pack is going live on June 27 for $14.99.
The pricing by itself is kinda surprising. It is quite a low price compared with other pricing models for other Blizzard games. In addition to the new hero, two stashes, two slots, and the other cosmetic perks (for $14.99), Blizzard is also giving you new areas: Shrouded Moors (Act II), Temple of the Firstborn, Realms of Fate (Act IV); plus the Greater Rift Challenge Mode feature-- these are provided to the players for free in the upcoming Diablo III patch 2.6.0.
Personally, I don't think there will be a Diablo IV any time soon. For example, StarCraft II is a 6-year old game that went through three episodes (if we may call them that): Wings of Liberty, Heart of the Swarm, and Legacy of the Void. Then, Blizzard released a three-part pack: Nova Covert Ops for ... $14.99. Is that pricing model familiar? Then they also release a new Co-Op Commander every few months for $4.99.
With Hearthstone, we have at least three major content releases per year, including expansions or adventures. I think they are scrapping the adventures from now forward, but there will still be three major content packs per year.
Heroes of the Storm and Overwatch follow a different pricing model, so I'll just ignore those for the time being.
Diablo III has only had the Reaper of Souls expansion -- and that was originally released on March 25, 2014. It is being three years since we saw new content, and suddenly Blizzard introduced the Rise of the Necromancer pack for $14.99.
Of course, there have been a couple shake ups throughout the lifespan of Diablo III, such as game director departures: Jay Wilson, then Josh Mosqueira (who stepped down to join Rob Pardo's Bonefire Studios).
What I think is going to happen, and this is me theorycrafting is that Blizzard might release new Hero packs like the Necromancer in the $14.99 model + free content every 1-2 year(s), and possibly more expansions. I don't think there will be a Diablo IV, the same way there has not been yet a Warcraft IV.
What I think is going to happen is that we might see a Diablo Online MMO at some point. There was something very peculiar about what Jay Wilson said many years ago:
[bluepost]JAY WILSON: "Diablo III" ends the trilogy, fans needn't worry -- it's not the final curtain for "Diablo." "We're not saying this is the end of the 'Diablo' universe, but we are trying to bring this storyline to a close," Wilson said. "It's not just 'Diablo III' -- we've got plans beyond." -- MTV Multiplayer[/bluepost]
So it is safe to say that before Jay Wilson left, there were plans set in motion, not only for the later released Reaper of Souls, but more beyond. We know that with Malthael destroying the Black Soulstone, Diablo and the other Prime Evils, and Lesser Evils are now loose. One of the cinematic cutscenes show that the hero that defeat Malthael might be possessed by Diablo in the future -- like he did with Aidan. So there is more story to be told, and a simple Hero pack like the Necromancer pack won't be the platform to tell such a story. It will require new Acts, and new zones.
What the Rise of the Necromancer pack opens is the possibility to see the Druid pack, and the Amazon pack -- for example, and new Diablo III expansions to expand the world. By that I mean adding Skovos Isles, Xiansai, Scolsgen, and the Torajan Jungles, the Dry Steppes, and the Swamp Lands. There is plenty of locations not visited in Diablo III.
The question is if we will ever see all of them in Diablo III, or if we will see them in a massive open world -- Diablo MMO. That doesn't even include the many other worlds out there beyond Sanctuary. Those who missed reading Richard A. Knaak's Diablo: The Sin War trilogy (2006) don't know there is actually canon knowledge that there are other worlds out there beyond Sanctuary. Voices from beyond halted the dragon Trag'Oul from intervening in the Sin War conflict informing him that the fate of Sanctuary would also affect the fate of their worlds. This has not been explored by Blizzard Entertainment yet, but it was obvious that this hinted there were plans for an MMO at some point in the future.
In the meantime, I think we will see more Hero packs, and possibly an expansion with new Acts within the next couple of years.