The primary focus of this build is to drop a Flamewall then swap into earth attunement and use the scepter to activate the fire combo field. Every scepter skill in earth attunement is either a physical projectile or a whirl finisher. Traits in earth are focused on damage, with +10% damage, 15% faster recharge, and 10% more damage when endurance is full. And in earth attunement with Rock Barrier, Stone Flesh, Signet of Earth, and 30 in Earth traits he should be fairly durable.
Speaking of endurance, that leads to the second focus of this build: Endurance regen. With pyromancer's Alacrity, and 20 points in arcane increasing boon duration I should be able to keep vigor from Phoenix up most of the time. Add Enduring Scepter and I can dodge a fair amount, and trigger Evasive Arcana.
I am aware of the apparent lack of synergy between Evasive Arcana and Enduring Damage, but my expectation is that I would dodge more against melee opponents, going back and forth across the Flamewall (which can be up 100% with traits) and Evasive Arcana should hit, since most dodge based traits from other classes appear to be PBAoE. Against ranged opponents dodging is not as necessary since I have Swirling Aura and Magnetic Wave, so I can simply stand behind my wall and get more bonus damage while ignoring most incoming attacks. I can still dodge any recognizable threats, and regen endurance to full quickly due to constant vigor and Enduring Scepter.
With minor master traits, arcane line, and evasive arcana the build should also spam a lot of PBAE without even trying. I expect there will be a short delay before going back to earth after refreshing firewall/phoenix, which gives me a good window to switch to water/air for whatever utility might be useful.
And then lastly I went into signets. Most of their abilities are redundant, more blind, more burning, and passive damage/toughness/healing. No need for signet of water with Phoenix and Magnetic Wave both with 15% faster recharge even. Signet of Earth -> Comet seems like a nice combo, since the Yogscast video seems to show comet striking multiple times.
I could replace the signets with anything really. But having simple redundancy and passives lets me focus on what the build is meant to do. Any signet could be dropped for a specific need. The only thing that feels lacking is mobility.