Currently, Wizard, Cleric, Druid, Bard, and Sorcerer all use the Wizard chassis for spellcasting.
What if: Warlock, Psion, Swordmage, Fighter-Magicuser, and Warlord all use the Warlock chassis for spell casting.
In the context of the Warlord, the "spells" are Per-Rest nonmagical martial "exploits" that use the spell format with the "Martial" spell school. Of course, these Martial exploits are nonmagical and cant be negated by antimagic effects. These Warlord exploits are normal "per short rest" exertions, or at-will "maneuvers" (cantrips). Meanwhile the "stances" are the Invocation design space that supplies various class features to choose from. A player can pick certain Stances to be a "Lazy Lord" Tactician who grants extra attacks to teammates and other buffs them, a "Medic" Inspirer to coach intangible hit points plus first aid triage and bandaging to deal with physical wounds when downed at zero hit points, as well as the Stances offering other class features to choose from. The high tier nonmagical equivalent of the Invocation design space may or may not be "per long rest" for the Warlord, and might be high tier Legendary stances, but whose power and effectiveness are equivalent to the highest slot spells.
In the context of the Psion, the spells are spells, but Innate. LaserLlama and KibblesTasty have popular Psion classes that use the Warlock while converting the Warlock slots into spell points − successfully. Both have excellent reputations and widespread usage at D&D tables. I prefer the design by LaserLlama for its straightforward choices and points that are more on par with other casters. Those whose tastes prefer "fiddly" might prefer the KibblesTasty design. Both class designs are solid.
I suppose the Fighter-Magicuser is what the 5e Eldritch Knight should have been. The name "Fighter-Magicuser" is a working placeholder. This flavor is the old school (High) Elf combat tradition that multiclasses in both magical wizardry and nonmagical martialism. Other cultures like the Githyanki "Gish" are also known for this class. Where the 2014 Eldritch Knight is incompetent at both spell casting and at damage dealing, this Fighter-Magicuser class uses the Warlock chassis but has fewer spell slots. The slots still advance to the same slot levels as a full caster. The slots that are missing have nonmagical Martial features instead. It is something like a "Blade Lock" multiclassing with a Fighter. It has only one Arcanum slot that can be used for spells of slot levels 6 thru 9, while any of these spells automatically augments to the slot level of Arcanum slot that upcasts it.
The difference between Swordmage and Fighter-Magicuser is, the Swordmage is truly a mage and is a full caster. The Fighter-Magicuser is a partial caster who is competent at both martial and casting, the casting is high tier but less frequent.