I was working on unique subclass ideas before the real ones were revealed (the Scorcher Titan was the only one that I was happy with. My Arc Warlock was almost complete, but the reveal kind of made it obsolete. And though we still don't know much about the perks, the class likely won't implement some of the awesome potential of a combat medic that I had in mind. That said, I realized that there is another way that classes could increase their diversity, and the way encounters could also have variety:

Overcharged Supers.

Tired of hoarding your Radiance because you don't know if/when you'll die?
Wish you could help your teammates defensively, but you've got a primarily offense-based Super, or vice-versa?

Well now there is!
Hold the Super activation button down to start charging your Super.

It takes three seconds to charge, and makes a distinct sound, alerting your PvP enemies that you're in a Vulnerable state, and that the situation is about to change drastically. As you hold it down, your super meter will fill with a vibrating white light. If you release it before it's full, you'll pop your regular Super. Once it's over halfway charged, you'll pop out into third person as energy courses through you. The longer you hold it after it's fully charged, the slower your character moves (and the meter fills with a red light), until they can no longer contain the energy, and then they explode (about seven seconds after it's started to charge), killing themselves, but dealing elemental damage of a similar capacity as a rocket. Cool? Yes. The point of the ability? No.

Popping it once the meter is full will unleash an ability that is unique to each subclass:

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Warlock:

Voidwalker-
Generous Vampire: Fires a slow-moving Nova Bomb that has a similar effect to a Vortex grenade against enemies, but grants teammates a Void-based overshield while they are inside (or for two seconds outside, but shield must fully deplete before being granted again). Damaging an enemy with the Bomb triggers health regeneration. Depending on Voidwalker perks, it can track enemies, cause them to explode, or increase in size/duration. Lasts five to seven seconds.

Sunsinger-
Hellfire: Coats a room (or large area if out in the open) with flames for seven seconds. Depending on Sunsinger perks, Flames can ignite enemies, Sunsinger can be greatly resistant to damage while inside Hellfire radius, teammate cooldowns can be greatly improved, and Brimstone causes all enemies killed by Sunsinger to explode.

Stormcaller-
Lifeline: fires arcs of lightning that can revive dead allies at range (even through walls), and grants them a powerful overshield for two seconds (prevents them from getting insta-shotgunned). Nearby teammates are also granted a powerful overshield for three seconds, and all shots do arc damage for seven seconds. You drop two Orbs of Light for every Ally revived, and revived Allies drop Orbs.

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Hunter:

Gunslinger-
For A Few Shots More: Amount of Gunslinger shots are doubled, doing half damage, but shooting teammates with them grants a five second damage boost (all teammate rounds do solar damage, with a chance to ignite enemies). Keyhole perk can chain the buff to more teammates. Circle of Life Kills while Overcharge is active grant more rounds (One per throwing-knife kill), allowing duration and damage to be chained further. Critical throwing-knife kills also drop Orbs of Light.

Bladedancer-
Improvise. Adapt. Overcome.- Player stays in first person, but movement and revive speeds are doubled. Jump distance is increased, all melee hits do increased Arc damage, and grenade cooldown speed is increased. Encore increases the duration from any kills, while melee kills can trigger Hungering Blade (if active) and generate Orbs of Light. Blink Strikes leave a shadow holgram that draws enemy fire. Agility rating greatly affects movement speed. Lasts for seven seconds.

Nightstalker-
Take Away All He's Got: Player shot anchors to all visible enemies, disabling their equipped weapon, shields, and grenades for five seconds. Minions of the Darkness have their elemental abilities disabled, and melee-based enemies deal half damage for seven seconds. Kills during Overcharge drop Orbs of Light.

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Titan:
Striker-
Live Current: Arcs of lightning track targets near Titan, triggering health regen on all teammates, while dealing constant damage to enemies. Movement speed is increased, and enemies killed by Current have a high chance of dropping Special/heavy ammo. Shoulder charge kills cause enemies to explode, while Unstoppabe increases Damage resistance. Death From Above doubles Lift duration. Lasts five to eight seconds (Aftermath increases Duration).

Defender-
Shattershield: Deploys a much larger dome for seven seconds while sending out a pulse that disables enemy shields (and momentarily stuns minions of the Darkness), and greatly reduces their recovery for five seconds. Each enemy killed within the dome triggers health regeneration for all teammates within the dome. Dome does not stop outgoing or incoming damage, but grants teammates Void damage for the duration of the bubble. Normal defender perks apply. Kills from within the dome drop Orbs of Light.

Sunbreaker-
Seething Rage: Titan Smashes Hammer into ground, sending out a blast that covers a large area. Blast causes Minions of the Darkness to attack all nearby targets (friend or foe). Armor is greatly increased, all kills grant stacking melee damage buffs, and all incoming damage received increases weapon and grenade damage. Friendly-fire kills and melee kills drop Orbs of Light. Allies within the Blast Radius receive greatly increased Recovery for ten seconds.

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I love being able to change up the battlefield for a short period of time. Overcharged supers could demand skill and timing, while adding unique changes to the sandbox and giving people an incentive to sacrifice their Super for some great risk/reward strategies.

I also think that the Kamikaze explosion alone is great, because it affects how enemies react to hearing the charge.
Do you run in and interrupt the Super, risking the person overloading it and killing you in an explosion, or let him pop it and shift the battlefield? Can you stick the Titan with a grenade and avoid his Fist of Panic, or will the Warlock catch you in the Hellfire?

And if you're the one charging it, do you risk getting killed as soon as you pop it, or try to sacrifice yourself with an explosion? As a Stormcaller, will reviving your teammates be worth dying?

Lots of stuff to consider.

One of the things that has always bugged me about how supers are balanced is that some of them allow the player to "roam" about the battlefield with their super active (gunslingers, bladedancers, sunsingers), hunting down enemies and taking out swathes of them at a time, versus the one-time-use supers that are far more situational (striker, and to a lesser effect voidwalker).

It would be cool to have this "charge" mechanic be a thing that allows all sub-classes to have one of each variant - a quick, immediate "panic" super, versus a charged, more prolonged super that opponents have a chance to shut down before it begins (eg. Golden gun or Arc-blade)

While I like the idea of "charging" supers for different effects, the Hunter Class is somewhat unique that both their current supers have a 2-3 second delay while the animation occurs before you can use them. The only other class that has that drawback is the sunsinger.

My first thought on your post was that you wanted something like the overcharge beam from R-Type, which would also be cool.