With the elemental invasions going on, I thought of a case-use for Nether Tempest that would make it viable, for all mages. Here it goes:
First: Yep, move it to the Mage tree. Swap it there for Greater Invisibility. Move Time Anomaly/Time Warp up a spot, and make Nether Tempest a 4 point spell down the center, like Meteor…
Next, give Frost mage a spell like Firefall in the Frost tree. Frostbolts call down a Comet Storm after so many Frostbolts. Put it in the spot where Comet Storm is now.
Move Comet Storm to the Mage tree. Put it down the Frost line where Meteor is. Maybe move Shifting power to the “branching node (hey it’s an Ardenweald ability” and Comet Storm to the outside node where Meteor is on the opposite side. Make Freezing Cold or Ring of Frost a selection talent, or move one to the Frost tree.
Finally: Give Nether Tempest a clause where casting a Meteor into it automatically summons a Comet Storm, or vice-versa.
Nether Tempest is weak on it’s own, but it’s found use in the Arcane build when TotM with Arcane Echo is up, you throw a Meteor down and watch those echoes go. That’s great for Arcane, and this would make it even stronger. It doesn’t make much sense to cast it outside of that, so it could be a 45 second spell. BUT… if Fire and Frost mages were to monitor their Firefall (let’s call it Frostfall) stacks, they could cast Nether Tempest when it’s getting close to a free Meteor/Comet Storm. So not having a cooldown is important.
Fire and Frost mages will pick up Nether Tempest to boost their Meteor/Comet Storm and Firefall/Frostfall talents, and Arcane Mage will just rely on Arcane Echo to make Nether Tempest viable.