It is possible, that blizzard even after Shadowlands, could really go full on one class only, with the specs reverting to being more like talents that only slightly alter the playstyle.
Question is, what then becomes of multi-roled classes ?
Do they:
1. Maintain specs just for those classes and develop those specs like they were classes
2. Turn those specs into actual classes too
3. A bit of both, i.e. keep Warrior /Priest/DK/DH the same, but split Monk/Druid/Shaman/Paladin into new classes
Each of these options will result in a reduction of playstyles to manage:
Which would you prefer?
For point 3:
Monk, Shaman & Paladin becomes 2 classes each: One with tank/dps spec, one with heal and dps spec
Druid becomes 3 classes: tank/dps (feral/guardian) healer/dps (with undergrowth themed dps ) , balance class.
Go from 12 to 16 classes with small measure of specs
[effectively down from 36 to 20 playstyles to balance]
For Point 2:
It would mean, Warrior/Priest/DK/DH all split into 2 classes, Monk/Druid/Shaman/Paladin into 3 classes, Druid into 4 classes.
A tank class like Guardian, Protection, Vengeance will have sufficient dps through talents to make you kill stuff fast enough for levelling and WQs, however you'll need the tank talents for raiding and dungeons.
Go from 12 to 20 or 28 classes - but no specs
[Effectively down from 36 to 28 or 20 playstyle to balance]
Complexity:
Concept shifts in this re-shuffle: Classes return to the classic level of simplicity. Talents are what give variation to playstyle and are a little bit more complex as there are no more specs.
The main complexities come with the expansions: Legion's artefact weapons system, BFA's Azerite system, Shadowlands: Covenant system - now as we all know each of these get really complex, look at Azerite now, you have abilities on Azerite gear, the necklace has abilities, and now corruption and legendary also has abilities. This is where the complexity and variation comes, and each expansion blizzard gives you a new system to build your class up during that expansion. As for levelling, it is quite straightforward, but if you want a more complex experience choose to level in Legion, BFA or Shadowlands so you can enjoy their systems. Once you start the new expansion levelling range, you are stripped of those powers.
Example of New classes:
This is the example of the full 28 classes that could result in from option 3, if we go with option 2, the former dps specs become 1 class rather than 2 separate classes
Warrior Classes
Beserker - formally fury Warrior
Blademaster - formally Arms Warrior
Warrior - the Protection spec (swapping shield for weapon boosts your dps a lot)
Priest Classes
Locus Walker - formally Shadow priest
Sunwalker - formally Discipline spec
[Priest - the holy spec is now the priest spec, talents can add some more damage spell and dps]
Warlock Classes
Necromancer - formally the Unholy DK (switches to cloth too)
Blood Knight - formally the Bood DK
[Death Knight - the frost spec carries the class]
Druid Classes
Valewalker - formally the balance spec
Botanist - formally restoration
[Feral/Guardian - Druid Class ]
Alternatively:
Star Augur - formally the Balance class
Shapeshifter is Feral & Guardian spec
[Restoraton is the Druid class]
Shaman Classes
Chieftan or Faresser - formally the Enhancment spec
Elementalist - formally the Elemental spec
[Resto spec is now the Shaman ]
Paladin Classes
Templar or Exarch - formally Retribution spec
Anchorite or Templar - formally the Holy spec
[Protection spec is now the Paladin
For the 2 class option: Paladin (Prot/Ret and Templar (Holy)]
Demon Hunter Classes
Fel Lord - formally the Vengeance spec
[Havoc - remains the Demon Hunter]
Monk Classes
Brewmaster - formally the Brewmaster spec
Runemaster formally the Mistsinger spec
[Windwalker is the Monk class]
It is very unlikely that the pure dps class specs will become separate classes. However some might. my bet would be:
Hunter:
Beastmaster spec remains the Hunter
Marksmanship spec becomes the Ranger class
Survival spec is split between the above 2.
Warlock:
Affliction: spec becomes the Witch Doctor class
Demonology is now the Warlock
Destruction is is baked into demonology
Mage:
Arcane spec becomes the Arcanist class
Frost/FIre becomes the Mage class
Rogue:
Outlaw becomes the Pirate class
Assassination becomes the Assassin
Subtelety is the Rogue