(TL;DR version at the end of this post.)
I want to see a "Halbu/Jamella" class in the expansion. I don't know if there's any canon lore about ex-mortals in the High Heavens, so here's a rough draft speculative back story:
When the Archangel Tyrael fell to Sanctuary, he not only unwittingly unleashed hordes of the angry undead, he also resurrected some of Heaven's greatest mortal champions. These warriors of the Light were allowed special entrance into the High Heavens, tending to Auriel's gardens, Itherael's library, and the other heavenly realms. (Imperius seemed to merely tolerate their presence, for he believed that even the lowliest angel should rule over something in Heaven.) Back in Sanctuary, the Resurrected have found a reborn purpose to their existence. After centuries of mundane servitude in the High Heavens, the Resurrected can now continue their war against the Burning Hells!
"Hail to you, Champion!"
Anyhow, the "Resurrected" class (alternatively, "Heaven's Champions") would be similar to the original Diablo's "blended" classes (i.e., a Warrior could cast spells to some degree of success, a Rogue could fight melee, a Sorcerer could shoot arrows, etc.). Their skills would run on a split combination of "Hope" and "Destiny." Some active skills would temporarily boost different stats, using slower-generating Destiny. Other active skills would be old Diablo spells, using quicker-generating Hope. Some passive skills would boost stats longer -- as long as certain skills are selected. Other skills or skill runes would lessen the cool-down period for health potions, bringing back the potion spam-type of game play.
The Resurrected would be able to equip weapons and armor from any class, but with less effectiveness. Furthermore, weapons and armor would have both level and minimum strength/dexterity/intelligence/etc. requirements for this particular class. Passive stat-boosting skills are a necessity for the Resurrected.
Also -- slightly off-topic -- if we get to actually fight Imperius in the expansion, he'd need more than angels on his side. One new enemy could be the Soulmate, inspired by Plato's concept, in which (quoting Wikipedia) "humans originally had four arms, four legs, and a single head made of two faces, but Zeus feared their power and split them all in half, condemning them to spend their lives searching for the other half to complete them." To modify for the Diablo universe:
In truth, Imperius not only tolerated the existence of elite human souls as servants in Heaven, he secretly experimented with them. In the dark corners of his Halls, the Archangel of Valor attempted to purge the demonic side of the souls of his Nephalem servants. He found that doing so created unstable beings that could threaten his realm. As a solution, Imperius merged two unstable souls together and created a secret army of these so-called Soulmates, just in case...
(Alternatively, Soulmates could be minions of Malthael, created during his madness in the Realm of Pandemonium.)
Soulmates would look translucent, like the Monk's Mystic Ally, but would have two faces, four arms, and four legs, like Plato's description above. Like the Mystic Ally, these Minions of Valor (Wrath) would come in different elemental varieties. After your character kills a Soulmate, there would be a chance that one half would survive and continue attacking (like the zombie torsos in Act I). Alternatively, the surviving half would be volatile and eventually explode.
Thanks for reading. Cheers!
1. Human souls in the High Heavens?
2. Halbu/Jamella/Diablo-throwback "open" class called "The Resurrected."
3. "Soulmates" as Imperius' or Malthael's minions.