Unless shield canceling and other similar animation exploits are patched, don't expect this to happen since while lockdown is unbalanced as is, this would just turn the game into a giant toothpick match.

Also variety in weapons is good, having a weapon type that does all different types of damage would be boring.

Some people like their mechanics, some people do not.
I like the Flourish as a weapon. I just don't like the fact that its sheer power, speed and versatility makes it the optimum sword of choice for LD; nevermind the fact that the piercing version is bad enough, you had to throw in elemental and shadow flourishes too.

In Lockdown, I hear that defenses towards shadow / elemental / piercing does not make a huge difference.
Tell that to me as I come at you guns ablazing with an Umbra Driver, and you with no Shadow defence whatsoever.
Mind you, even that can wipe out strong Strikers in a few hits.

Regardless of it making a difference, this game is in fact more PvE oriented and created based on PvE.
Unless you want the swords in question to have separate mechanics for PvP and PvE, which will be deviously difficult to code, I don't see how this will be implemented anytime soon.

It would open up more options for swordsmen for shadow and elemental swords.
Unanimously we can agree that swords in general have the highest DPS of any weapon type in game (save for one specific gun); for this fact alone there can't be too many shadow or elemental swords.
That being said, I am open to having more of these swords, provided that they introduce new weapon mechanics into gameplay, as you mentioned in your post.

If I want to get picky, we actually need an elemental DPS (nitronome-like) bomb that does not create knockback (similar to DBB) but that will be in another thread that I create.
This, coupled with the fact that you want shadow/elemental Flourishes, seems inherently contradictory to your statement that we need new sword mechanics.
Again, what we need are weapons with new attack mechanics; though not so much for bombs since there's only so much you can do with them.

I think what we need are more diverse playing styles, not remakes of old swords in different damage variants.

No new flourishes. The old ones are already broken.

Fast hitting pure damage on a sword is already troublesome, but the first swing is a wide sweeping attack, which makes absolutely no sense for a piercing weapon and unbalances it for both pve and pvp.

It is fun to use though.

I agree we need more variety in weapon mechanics. However, I have recently pondered which of the three deserves greater variety due to lack thereof. We have three weapons with various mechanics identifying them as one sub-type. The following may explain.

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Sword: 6

Standard: three hit, regular speed, fairly small swing range; Calibur, Brandish, Beast Basher, Slime Slasher, Hot Edge and Static Edge lines, Fang of Vog, Scissor Blades, Wrench Wand.

Heavy: two hit, slow speed, large swing range; Hatchet, Sealed and Troika lines.

Foil/Rapier: three hit, great speed, first hit has a large swing range but the two following are fairly thin in exchange for greater stab range in the direction the user aims; Flourish and Snarble Barb lines.

Cutter: five hit with one after-hit after each swing, moderate speed, slightly more swing range than standard due to the after-hit making contact slightly further; Cutter line.

Spur: three hit (when upgraded to Winmillion each swing also fires a projectile), regular speed, same swing animations as standard with more range; Spur line.

Rocket Hammer: three hit (the second hit is a slide which also damages enemies which make contact), the first and third swings are the same as heavy swords but with more speed; Prototype Rocket Hammer, Stable Rocket Hammer, and Warmaster Rocket Hammer.

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Gun: 7

Standard: three shot clip, charge attack releases a single bullet with more damage than regular shots; Stun Gun and Blaster lines, Proto Gun, Frost Gun, Zapper.

Alchemer: two shot clip, (when upgraded to 3* and higher the bullets will bounce off of objects hit), charge attack releases a larger bullet (this large bullet releases smaller bullets after the large bullet is consumed, varies by rank); Firotech Alchemer, Cryotech Alchemer, Prismatech Alchemer and Shadowtech Alchemer lines.

Magnus: two shot clip, high bullet speed, user may not move while firing, firing causes the user to move back slightly, charge attack fires a larger bullet and recoils the user in knockback and knockdown; Magnus line, Punch Gun.

Autogun: two shot clip (each shot fires several bullets), moderately fast bullet speed, user may not move while firing, charge attack releases a floury of bullets for an extended time compared to the basic attack; Autogun line.

Pulsar: three shot clip, slow bullet speed, bullets expand and explode when allowed to travel a short while after being fired (expanded bullets cause knockback and increased damage compared to hitting the target before expanding); Pulsar line.

Catalyzer: three shot clip, slow bullet speed, charge attack tags orb mines on the target which may be detonated by any Catalyzer (intended for teamwork where one knight tags the target and the other detonates); Catalyzer line.

Antigua: six shot clip, high bullet speed, charge fires several bullets before a large bullet (when upgraded to 5* the large bullet changes to an owl) which pushes enemies away; Antigua line.

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Bomb: 5

Standard: normal blast range, damages targets within the area of effect; Blast and Spine Cone lines, Firecracker, Cold Snap, Static Flash.

Vaporizer: normal blast range, damages in a very small area around the epicenter, leaves a status inflicting mist in the blast range; Fiery Vaporizer, Freezing Vaporizer, Toxic Vaporizer, Static Capacitor, Haze Bomb lines.

Crystal: incredibly small blast range, fires projectiles in eight directions (north, northwest, west, southwest, south, southeast, east, northeast) a long distance; Crystal line.

Suction: small blast range, creates a suction vortex after the initial explosion (enemies take a small amount of damage when affected by the suction) which explodes and releases the enemies close to the epicenter; Graviton Charge and Electron Charge lines.

Dark Reprisal/Seerus bomb: small blast range, creates four orbs which circle around the epicenter (the initial explosion damages the epicenter) in two orbitals; Dark Reprisal, Dark Reprisal Mk II, Dark Retribution.

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Final Score

Gun: 7
Sword: 6
Bomb: 5

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I have nothing against more variety with swords but in this thread we have four types of what may be a fourth weapon type or sub-culture of swords as melee weapons.