Since we ran out of weapon ability altering sets, maybe its time to add class ability altering weapons?

How it's gonna work
Classes use different weapons, so it's logical that this 1-piece set should drop in all weapon variant. And the same as weapon ability altering, these will alter the class specific skills, so they also need to be for all 3 class skill lines. Since this would lead to some crazy RNG to get exactly thing you want, I suggest adjusting content so it will drop one piece per skill line all at once.
For example some solo or 4 man arena divided into 3 zones, where you fight some long ass boss fight and each gives weapon for the each skill line then you fight 4th one that drops weapon or accessory for altering the class ultimate or something.

What about skills that drastically change its functionality?
Give it effect that is independent, like Master Destro spell damage boost

Examples of the effects

DK:
Lava Whip: Lava Fury - gives the Seething Fury stacks to both morphs with 20% instead of 33% increase, but stacks dont expire on cast. Overwrites Molten Whip Seething Fury.
Spiked Armor: Spiked presence - Spiked Armor looses it's "thorn" mechanic, instead it pulses every 2s dealing flame damage equal to % of Armor for 10s.
Stonefist: Landslide - Stonefist is no longer ranged, instead it heals or deals damage in 5m radius around the target.

Sorc:
Summon Unstable Familiar: Unbound Familiar - pet is no longer permanent and removes cast time. Pet periodically activates its ability itself with no cost (Clanfear heal need to be changed somehow otherwise stamsorcs will be immortal)
Crystal Shard: Crystal Blast - special proc stuns the target and deals damage in 5m radius. Crystal Weapon permanently has AoE but doesnt stun.
Mage's Fury: Rising Voltage - no longer procs explosion, instead it incorporates into base abilty damage that scales up from 90% of target hp.

NB:
Assasin's Blade: Backstab - Assasin's Blade deals up to 100% additional damage to low hp targets when attacking from behind.
Veiled Strike: Opportunist blade - Attacking Off-Balance targets applies additional bleed dot.
Strife: Essence funnel - Critical hits makes next Strife instant, undodgeable and heal for additional amount.

Templar:
Puncturing Strikes: Empowered Strikes - each jab increases Spell and Weapon Damage by 30, stacks up to 5 times for 5s.
Sun Fire: Prism rays - Sun Fire bounces to nearby targets up to 3 times, grants Major Sorcery and Brutality on hit
Rushed Ceremony: Completed ceremony - reduces healing by 10% but heals all targets in a cone in front of the caster

Warden:
Dive: Winter's Shadow - Casting Dive causes to cast additional Dive that deals Frost damage equal to 50% of the damage original Dive did. Dot from Cutting Dive's shadow also deals frost damage.
Fungal Growth: Fungal Glade - Shrooms heals in a circle instead of cone.
Frost Cloak: Frozen Shield - while Frost Cloak is active, gain 10% additional block mitigation. Allies gain damage shield equal to 15% of your max hp.

Necro:
Death Scythe: Wraith's Scythe - Throws the Scythe at target location, deals damage to every target on the line to destination, then deals extra damage in small splash.
Flaming Skull: Giant Skull - each hit applies disease damage dot. Every third cast creates a corpse.
Render Flesh: Rotting Flesh - Render flesh deals damage equal to amount of hp healed around target. Applies minor defile to all targets hit.