Another thing I kinda hoped that 5e would dive in is the idea of natural talent vs trained skill vs granted/borrowed power in the fantasy universe.
You'd have the naturally talented warriors of the barbarian and ranger who have their natural talent focused in a direction and are taught ways to supplement and harness their raw ability. Then you have the trained skilled warriors of the fighter, monk, and warlord who use practiced techniques that could be taught to anyone of decent ability. Finally you'd have the paladin and "arcane paladin" who are given power and then taught to wield it. Or the barbarian/fighter/paladin could be the pure 3 with the ranger, warlord, monk, and "arcane paladin" as hybrids.
We see the strengthening of the trio from 4e to 5e in the arcanists with the sorcerer, wizard, and warlock.
Then there could be a Talented vs Skilled vs Gifted trio for the "skillmonkey" classes. The Rogue exists as the learned "skill user". This opens up the concept of a talented acrobat or dancer class for the naturally dexterous or a super-genius sage class for the mental savants.
----
There are many opening for new classes for 5e. Don't it need them? No. Should it get more classes? Maybe.
5e is almost already at the point where its can't think of completely new ideas for subclasses. It feels to me that 5e is now just squeezing the classes it has for juices within the constraints with just changes of elements, subtypes, sources, and origins. It'll need a new class if it go 5 more years officially.