The jack of all trade aspect of the Elementalist has always been one of its strong points, but also its biggest weakness. As pointed in You can't design a hybrid class like ele and expect it to work, the hybrid aspect of Elementalist clearly does not work and is tremendously hard to implement properly.
I believe the problem does not necessarily reside in the Elementalist being a multi-facet class, but by being TOO much of a multi-facet class. Having access to an AoE damage element, a CC/damage element, a sustain element and a survival/CC element AT THE SAME TIME is what I believe hurts the potential of the class. Elementalists cannot be allowed to shine in any of those aspects because they have too many other features to back it up and could easily degenerate. It also makes coming up with a specialization hard and fuzzy, as we've seen with the two previous ones (probably my two least favorite specs of the game). They do not specialize the class but try to maintain its quad-element-good-at-none facet. This is why I'm proposing a new approach today.
Another problem is the fact that having only one weapon, they can only be full melee or full ranged. Unlike all the other classes that have access to both, Elementalists are locked behind one range and being squishy, they struggle to survive melee if they wish to deal decent damage in any competitive player vs player game, which is why they are currently the worst possible class for PvP and roaming WvW.
The Imbuer / Dualist (I couldn't come up with a better name yet so I'll just call it Imbuer for now) sacrifices two elements in order to fully master the remaining two. In essence, they lose their natural versatility in other to be allowed to access other sorts of versatility, more ranged based.
Wielding a trident as a two-handed weapon, they channel their elemental wrath through focused meditation in order to augment their affinity and conjure the wisdom of the missing ones.
They can choose two elements to attune (kind of how revenants choose their legend). They lose their F2 to F4 attunement swap in exchange for only an F1 skill that swaps between the two. They also have access to a new F2 skill and a gauge mechanic. Fighting fills the gauge (similar to holo's heat or warrior's adrenaline).
Now, I've come up with two takes of the class so I'll list both and wait for your suggestions and input.
I believe option 1 could become really complicated and might overtune the specialization, forcing it to be toned down in other aspects to prevent it from being OP and thus, coming back to the same problem as now. This is why I've come up with another idea instead:
You have Fire + Air as your elements. You are attuned to fire and your attacks fill your gauge. Wielding a trident, you have 300 range max (maybe less?). When activating your Imbue skill, F2, your attacks consume that gauge at a rate that depends on the skill (Say, #1 uses 3%, #2 7%, #3 10%, #4 20% and #5 30%) and add a secondary element effect.
Say, Trident #2 on Fire is a thrust forward that does damage and burn. When imbuing, the skill has a 900 range thurst, the first 300 doing fire damage and burning while the remaining 600 doing air damage (animation wise) and maybe inflict weakness? Or Trident Fire #5 is a rapid whirl that does AoE damage around you, the imbued version extends to a 480 or 600 radius and blinds in that area.
It would give access to a consistent and varying range, something that Elementalists are the only ones lacking currently. (Staff is absolutely useless in melee for PvP).
Something that could go nicely with that is Meditations / Physical / Trick. They would give access to some utility and mobility skills, that would depend on the chosen elements.
The healing and elite skills could use the missing two elements and the 3 utilities would grant an effect depending on your equipped ones. Here are some examples/suggestions.
Healing skills Prayer to the Forgottens (3/4s cast, 25s CD)
Call upon your missing attunements to heal yourself and provide an effect to you, depending on the missing elements.
Missing Fire: Remove 2 boons from your enemy
Missing Air: Break stun and grant superspeed for a few seconds
Missing Water: Remove 2 damaging conditions
Missing Earth: Remove 2 movement impairing conditions
Example: You have Fire/Air attunements equipped, leaving you with no access to condition removal. The healing skill would remove up to 4 conditions from you, providing you with a little bit of cleansing (could tune down the number to 2 instead of 4, if it ends up being a lot).
Utility #1: Elemental Assault (1/2s cast, 20s CD)
Dash forward a bit (300 range maybe), the attack gains an effect based on your current element. If your gauge is above 50%, gain your secondary element effect too.
Equipped Fire: Blind foes in your trail
Equipped Air: Shadowstep mid-dash to your target (150 then it shadowsteps for 600 range max and finishes the 150 remaining, extending the range to 900. Kind of like Shiro's dash)
Equipped Water: Chill foes in your trail
Equipped Earth: Evade attacks during the dash (1 sec)
Utility #2: Attuned Counter (25s CD)
Break stun and prepare to evade the next attack for 1 second. If you're attacked during that window, counter with your primary attunement. Above 50% gauge, gain a boon based on your secondary attunement.
Equipped Fire: Counter - Inflicts heaving damage and burn your foe. Boon - Gain 2 (50% gauge) to 6 (100%) stacks of might for a few seconds.
Equipped Air: Counter - Inflicts heaving damage and stun your foe. Boon - Gain 1s (50%) to 3s (100%) of quickness.
Equipped Water: Counter - Inflicts moderate damage and transfer 2 conditions to your foe. Boon - Gain 1s (50%) to 3s (100%) of vigor.
Equipped Earth: Counter - Inflicts moderate damage and knock down your foe. Boon - Gain 1s (50%) to 3s (100%) of protection.
Utility #3: Elemental Reversal (25s CD)
Convert 2 conditions into boons, depending on your current element. Above 50% gauge, convert 2 more depending on your secondary element.
Equipped Fire: Gain 1 stack of might for each condition lost
Equipped Air: Gain 1s of quickness (or superspeed) for each condition lost
Equipped Water: Gain 2s of vigor and regeneration for each condition lost
Equipped Earth: Gain 2s of protection for each condition lost.
Elite skill: Forgotten's Intervention (30s or 45s CD)
Call forth your lost attunements to assist you one last time, gaining a boon per missing element for a few seconds, double duration above 50% gauge.
Missing Fire: Gain 10 stacks of might for a 5 seconds.
Missing Air: Gain 3 seconds of quickness.
Missing Water: Gain 1.5 seconds of resistance.
Missing Earth: Break stun and gain 2 seconds of stability.
I've decided to go for a smaller effect, smaller CD Elite skill as elementalists have in general long CD with a bigger impact (Just kidding they have no impact, their current Elite skills are the worst of all classes). This way, you can weave the Elite skill more often, for a smaller but consistent impact.
There could be a grandmaster trait that grants the boons from the utilities to allies around, making it a strong support class.
The gauge specific boost above 50% of the utilities could also be a trait option if some tuning is necessary.
The idea of this specialization is to provide Elementalists with the means to focus on certain aspects. They can go heaving damage/CC with Fire+Air (possibly taking Fire+Air as traits), support or Water+Earth, mobility survival with Water+Air, damage survival with Fire+Earth etc. It offers them many options to specialize in SPECIFIC areas, rather than 1 option to be a bit of everything.
For example, a list of possible builds I can image running Imbuer:
WvW Roaming SF Air / Water: High damage Fresh Air with a bit of durability and condi cleanse
SPvP Trident or DF Water / Earth: Point holder with some team capability
SPvP DD or SF Fire / Earth: Condi with some durability
PvE Trident or DD Air / Water: Offensive support that provides some quickness and durability
If their two attunements are displayed from the get-go, they'd also have clear counter plays as you could easily tell what possible build an Imbuer could be running based on the situation and chosen elements.
The gauge mechanic idea was introduced in order to limit their bursting and survivability potential, even if you equip them with plenty of mobility (they're not thieves so they shouldn't be able to go in, OS and go out. The gauge makes it easier to balance around that.)
What they lose in complexity from the removal of 10 of their weapon skills, they gain in the F2 range modifier skill and gauge management, as well as keeping track of your attunement effects on your utilities.
Let me know what you think of this idea and if you would like to see it in the game, as well as any concern you may have. I'll try coming up with trident skills idea later, feel free to drop suggestions.