I would like Flame Orb... Frost Mages have Frost Orb as a massive AoE-Tool. They could give Fire Mages the classic Flame Orb dealing some cleave-DMG and a Arcane Orb for Arcane Mages dealing singletarget DMG.
Mage Ward would be nice but was kinda replaced by Ice Barrier for everyone.
Focus Magic would be a nice way to add some more "unique support" to the game like Stormlash, Banner, Tricks or Symbiosis.
Blast Wave... why is Blast Wave gone? Fire needs a cool instant AoE-Spell anyways. Sucks to only have CoC with Glyph really dealing instant AoE-DMG.