I understand that blizzard is trying to create sub specializations that take a flavor of 2 specs. I don’t think this hybrid spec system is thematically interesting or a good representation of what a “hero spec” should be. To start off being limited to what talent tree you can chose based off your spec is not a fun design in my opinion. What if I play a spec that does not have access to the hero spec I like? I suggest moving away from the hybrid system and allowing any spec to choose any hero talent tree. Secondly, the themes of the hybrid spec particularly the mage ones are very lame. Why would you choose any of those when you have things like necromancer/lich, chronomancer and archmage? All of which are well established in the lore. These are also easily integrated into any of the 3 mage specs.
My ideas for the new hero talents based off my suggestions for mage would be as following:
Necromancer:
Death borne, fully embrace death magic to increase damage done by X% for X seconds everytime you consume clear casting, hotstreak or brain freeze increase damage done by 1% stacking up to X times. This replaces arcane surge, combustion and icy veins.
Raise the dead, summon 3 skeletal mages that cast a copy of your spells at X% effectiveness for X seconds. This replaces mirror images.
Chronomancer:
Reverse time, return to a point in time 5 seconds ago restoring all party/raid members missing Health. This replaces alter times.
Time dilation, activating combustion, arcane surge, or icy veins accelerates times increasing X party members haste by X% for X seconds.
Archmage:
Choice node:
Frost fire bolt, hurl a massive bolt of extreme heat and cold at an enemy dealing X damage. Everytime you consume hot streak, clear casting, or brain freeze the damage of frost fire bolt is increase by X% stacking X times. X second cooldown.
Insight, consuming clear casting, hotstreak, or fingers of frost increases the damage of your next arcane barrage, fireball, or frostbolt by X% stacking X times.
Choice node:
Gift of the magi, casting a frost, fire and arcane spell within 10 seconds of each other infuses you with ultimate arcane knowledge increasing damage done by X % for X seconds.
(Insert current spec) mastery, increases (insert current spec) damage done by X%
These are the major thematic changes that could be made to make you FEEL like you are playing a HERO class, it’s also allows player to retain spec identity if they choose to with the archmage talent choices.