Straighforward to the suggests and the generic idea.
Scorch ( buff) : adds 20% of ignite passive damage into its damage as long its mostly a spell for finishers then it should get stronger as time passes and ignite grows higher. ( scorch will still have the 30% threshold but other than this it’s damage output will come mostly of fire Mage ignite passive)
Pyroblast : has increased 5% increased critical damage and each time your pyroblasts critical you gain 1 stack of Pyro Frenzy, at 3 pyro Frenzy stack your next pyroblast will be instant cast and will consume all pyro frenzy stacks inficting 10% incresed damage and 100% increased ignite ( more options about pyro frenzy into fire telent tree may exist). ( It should be your strongest single target burst with increased power based on critical)
Combustion ( new) : while you have combustion stacks : 75% of critical strike becomes mastery ( as it is) 25% of the critical percentage increase the critical damage you infict with fire spells ( if you have 40% critical chances then that 25% translates into 10% extra critical damage ). Combustion will give you 5 Combustion stacks. every 5 seconds your combustion stacks drop by 1 each time a combustion stack is being consumed or expires by timer that timer refresh. While you have combustion stacks your fire spells other than Fire blast and phoenix flames will consume one combustion stack gaining a gurantee critical and have increased 10% spell power. Different trees for combustion if you focus into single target damage or Aoe should exist. ( making fire Mage entirely a machine gun makes things too hard to balance so it should be a quick burst of high damage without being too extended)
If you consumed 5 or more Combustion stacks for casting spells. Then your next non instant flamestrike or pyroblast will have 30% decreased casting time and inficts 60% increased damage and has a gurantee critical ( that could be a fire talent instead).
Firefrost under fire mage tree ( generic idea ) : Targets under firefrost bolt effects take the ignite damage twice per second instead of once. When a fireblast applies living bomb on a target that is under ignite effects and firefrost bolt effects will make your next firefrost bolt instant cast, gurantee critical and ignores the global cooldown .
when you Critical hit one or more enemies with firefrost Bolt, pyroblast or flamestrike drops the remaining cooldown of Meteor and commet storm by 2 seconds. On addition each time your ignite inficts damage to an enemy has a low proc chance to decrease the remaining meteor and commet storm cooldown by 1 second.
Sunfury ( generic idea ) : Spell orb shards ( a little different way to generate spell orbs) : You generate 1 spell orb shard per second at 60 spell orb shards you gain 1 spell orb, your fire and arcane spells generate 5 spell orb shards , each time you consume a hot streak you gain 15 spell orb shards. Each time your shifting power drops your cooldowns also give you 10 spell orb shards.
Phoenix flames while the caster is within close ( not melee but close) radius of the alar will become alar flames instead of phoenix flames the fire mage casting alar flames will make alar be the projectile and move to the enemy hiting and inficting 20% increased damage. Alar keeps casting while moving this way also while moving alar becomes immune , this spell is castable while you are under stunned or silence like effects. Alar flames get affected by any talent passive ETC that affects phoenix flames.
When your alar first summoned fire mage refresh one stack of Phoenix flames. The first Alar flames that succesfuly hit an enemy after alar being summoned will make your next fire blast during the next 3 seconds infict 20% increased damage and stun enemy for 1.5 seconds and refresh one fireblast and one phoenix flames stack uppon hiting an enemy. When Alar time expires ( if it didnt die) will return to player as long player is within certain radius restore 30% of damage delt by fire mage Alar flames abilty and by total damage alar spells did.
This way your Alar can move so your enemies cant just outrun alar as long player can micro manange alar with phoenix flames ( Alar flames) giving a short healing that fire mage lacks.
thats generic ideas without moving too much into details about which talents may replaced or being buffed.