I've always wanted to see a sort of divine skill class, sort of a fighter is to rogue as paladin is to [this class].
Interesting. Yeah, I once (using PF) wrote down all the classes in kind of a 'grid' format using the four 'base' types - Warrior, Rogue, Mage, Priest.
Fighters and Barbarians are pure Warrior. So are Monks, really, though a very different kind.
Wizards and Sorcerers are pure Mage.
Clerics and Druids are pure Priest.
Rogues are pure Rogue.
Then the other classes are hybrids:
Bard (in older editions) is basically Rogue + Mage. In 5E, that's the Arcane Trickster subclass of Rogue.
In Pathfinder the Magus (the only non-core class I think was really worth having) is Warrior + Mage. In 5E, the Eldritch Knight subclass of Fighter fills that role.
Ranger and Paladin are both basically Warrior + Priest, though Ranger has a trace of Rogue in it IMO.
Which leaves Priest + Mage and Rogue + Priest unclaimed.
The other possibility I see 'open' is another Rogue-type. Fighter/Barbarian, Wizard/Sorcerer, and Cleric/Druid all have kind of a learned/civilized vs instinctive/natural dichotomy going. There's no pair like that for the Rogue.
Maybe the existing Rogue could be the 'instinctive' one and the new class could be the MacGyver/Gadgeteer/non-spellcasting Artificer other people have talked about on this thread? Not necessarily totally nonmagical though, it would use alchemy and stuff... is that 'magic' or fantasy-science?