So... having taken a look at units from WC-WC3 and mobs etc from WoW. I came up with a simple lift, no spiffy details :P Just stuff that kinda are missing. Some are possibly better of as specs, like a bloodmage for example.
Tinker
Fantasy: Gadgets, Mech Suits, random Tech.
Races: Human, Undead, Orc, Gnome, Dwarf, Draenei, Blood Elf, Goblin
Justification for races: All of these have shown interest or skill in engineering at some point or another, and inclusion is better than exclusion.
Reasoning: Tinker is a no brainer, it has endless possibilities because its only core tenent is Technology, and that is a superwide archetype. It's also a fan favorite of late.
Occultist
Fantasy: Forbidden Magic, Non-Demon related.
Races: Human, Undead, Blood Elf, Orc, Gnome, Goblin, Troll, Dwarf, Worgen
Justification for races: Anything that can be a warlock really.
Specs etc: Necromancy, Blood Magic, Runemaster
Justification: The vrykul in stormheim uses a kind of rune magic that seems easily expandable, blood mages have started popping up everywhere and they seem to be alot about giving life to things, necromancer is another fan favorite that due to death knight probably works better as a spec than a full class.
So far these are the only real options I have found that doesnt overlap with what we already have, if I notice more or if anyone else thinks there is something missing, comment etc... Just curious how people feel, since I see alot of "there are no more classes that could be added".