Over the years, you tend to see warlocks siding with various factions besides just the Burning Legion, whether that was with serving alongside Illidan in the Burning Crusade, the Twilight’s Hammer, the Hakkari, the Cult of the Damned, the forces of Ragnaros or even the Primalists — All in order to attain secrets of hazardous power!
“Behold those who have power, and who are not afraid to wield it. Behold… the warlocks!” – Gul’dan
Warlocks alignments & bids for power …
Such of the above makes sense, since many warlocks favoured the Legion in order to attain power for themselves - for their own best interests, rather than believing in the Legion’s cause — So having those with the same mindset but towards other factions that can grant them great power, yet perhaps with a better end-goal in mind that they can see themselves supporting more? 
That’d make far more sense.
I was hoping to see more of the “Practitioner of the volatile & dangerous powers!” emphasised with warlocks overtime, rather than just demonic & chaos magic — Such as:
- Necromancy – Bidding with the cult of damned for necromantic power
- Elemental – Bidding with the Primalists for elemental power
- Void – Bidding with the Twilight’s Hammer, Black Empire or Xal’atath for void power
- The Nether — Having warlocks even strangely help the Netherwing Flight — To delve deeper into the secrets of the nether, those which energies aren’t situated in chaos, but more harmonic; so they can use its purest forms of power towards the potential of their own power.
Getting demon / battle-companion skins that emphasise the aesthetics of the above, would be AMAZING! 
Example born from the above -
For the secrets yielded of the Primalists & Scalesworn Cultists, from the elemental powers attained you could have new summon visuals such as:
- Voidwalker – Shadowflame Elemental
- Imp – Firekin Grell … They look pretty much the same
lol
- Felhunter – Hell-hounds — (otherwise known as Flamehounds or Charhounds - Examples seen are Riplimb & Rageface from the Firelands raid)
- Succubus – Female Djinn — Example:
https://wowpedia.fandom.com/wiki/Air_elemental?file=Benevolent_Djinn.jpg
- Felguard – Fireguard – (Similar model to Smolderon but perhaps without wings)
You could then emphasise the aesthetics of such aesthetic or another into their spells, whether it’s shadowflame, thunderous-zappy power mixed with shadow or otherwise. 
The necromancy visuals I’ve detailed in another thread of mine from quite awhile ago –
Customisation for Warlocks: The OG Necromancers
When it comes to warlocks, I’d say for the void visuals – That the possibilities would be pretty simple to manifest into their variety of toolkit towards their demons, spells and so forth …
Much, much more!
However there’s so much more that could be utilised, like blood beasts — Born from blood magic – whether such was learned from Hakkar, the Blood Trolls or even some mad scientist sorcerer who’s knowledge we stole & unleashed to use at our disposal and benefit 
The secrets of the nether, utilised from the Netherwing flight could be an interesting concept to play with too – Giving us colour variations seen from the Netherwing drakes (the nether-lightning that crackles along their bodies) and that which is seen in the Netherstorm and Tempest Keep.
- Similar concepts of seizing the powers & knowledge of various factions could apply to other classes too, but for the sake of thread size I’ll stick to warlocks for now. lol
Anyway! What’re some exciting features from the secrets of the controversial factions, along with the forbidden powers & hidden knowledge — would YOU like to see come forward for warlocks or even to other classes 
along with the ability visuals or models (for pets / guardians / summons etc) would you like to see brought from them? 