Warrior> At level 10 you choose to be a Barb/Druid/Dragoon.
Rogue> At level 10 you choose to be a Amazon/Assassin/Monk
Mage>At level 10 you choose to be a Warlock/Sorceress/Witch Doctor
Priest(or something)>At level 10 you choose to be a Necromancer/Crusader/DeathKnight.
i like the idea of evolving classes.
As a game system it could be interesting.
Some sort of Class Development and Path Choosing.
But, when it come to Sanctuary Lore, it wouldn’t quite fit.
In Sanctuary, the different classes are part of their own “tribes”. Of course, there are a few exceptions, but, for example:
Barbarians, Amazons, Witch Doctors, Necromancer, Crusaders… they all have world lore that supports the birth of their people, their “tribes”.
A warrior doesn’t become a Barbarian as a rogue doesn’t become a Amazon and a Mage doesn’t become a Witch Doctor.
But… not to say I just come with problems…
The system it self could be implemented in a more specific way.
It’s a smaller system compared to your idea, but would fit better the in world.
And, of course, it should be permanent…
Fun idea.
I was playing with an idea of having a giant skill tree per class maybe brancing out in the middel… where each tab had different focus Off = Offensive, CC = Crowd Control, Surv. = survivability
Class
Warrior.
Skill/talent Tree tabs
Barbarian (off)
Paladin (Surv)
Gladiator (Off)
Monk (CC)
Dualist (Off)
Class
Spiritualist
Skill/talent Tree tabs
Necromancer (CC)
Shapeshifter (Surv)
Storm caller (Off)
Soul bender (Surv)
Witchdoctor (Off)
Class
Elementist
Skill/talent Tree tabs
Lightning (CC)
enchanter (Surv)
Fire (Off)
Ice (CC)
Arcane (Surv)
Class
Thief
Skill/talent Tree tabs
Martial artist (Surv)
Shadow Assassin (Off)
Ranger (Off)
Tactician(traps) (CC)
Acrobat (Surv)
This would bring some cool hybrid builds to life, and add a lot of personalization to the char creation… like back when WoW was new, you where recognized as a “Holy paladin” or Protection Warrior ect…
I agree more with that direction. They were trained as part of their own trive but that shouldn’t stop them for specialize or learn other stuff after.
I posted the idea of D4 Shared Skills that allow classes to pick off-class skills (not skills that belong to other classes but skills that arn’t of any class) after reach max level. This allow to create hybrid classes, giving the option to personalize even more your character and play style.
Some examples could be a mage that select skills that allow them to use melee weapons and more armor to create a melee-mage kind of class.
Nice ideas.
I Also had Another Idea how to make hybrid builds… that items,charm ect can have + skills but the only way you can use them is if you have the required resources…
Then you would need +resource +resource regen to use the skill…
It you have to much 2nd 3rd resource you get corrupted ( 3dmg/resource point ) or something like that 
Yes, i had the idea of have skills on items too. Maybe on mythic items (that way we only can have one). If other items can have skills too, then the most powerful ones should be only on mythic items and the less powerful ones on legendary items. I had the idea that ancient items could come back for this: the new ancient items would be the same as the legendary ones but with a skill instead of a legendary affix.
Nice… but what kind of skills…
something like
Mantras (monk)
Element Armors (Wiz)
WW (barb)
Werebear/Werewolf (druid)
I think it could be viable… because if we get skill points/talent tree multipliers then the +skill from items would be no where near the power of the origenal 
The idea for the Shared Skills is to make them unique (can be similar to existent ones) skill that don’t belong to any class. But the items on skills could be class skills or powerful no-class skills (only on Mythic items), but would need to be skills that fit with different classes.
For example, WW (barb) doesn’t require a specific weapon, so it is fine to have that one. If there was a skill that require a weapon that class can’t use, there it could come into play the Shared Skills (for example have a mastery for that type of weapon that allow the use of that weapon).