Ill try to guess, what kind of legendaries might be coming regarding the ones that are already there.
Greatsword
After The Twilight/Sunrise/Eternity trio we will probably get something less clean, more dirty, maybe tied to an element. I guess it will be a single, less flashy legendary this time but nonetheless an iconic one since Greatswords are something a lot of players use. A non-symmetric more scimitar like weapon that will probably be tied with fire since that would easily fit a lot of the armor in GW2. Something, magitechy, light-saber like with a cool sound effect is imaginable.
Staff
The other two handed weapon besides the GS that can be used by 4 classes. Probably the next double legendary. Having two opposites that combine into one.
I could come up with following opposites: ice&fire, Tech&Nature, Life&Death, Wisdom&Impuls, different opposing emotions. Since I think that the legendary GS will have a fire theme and a “tech staff” would probably not be very liked amongst the caster classes, Ill go and guess there will be a tree-like life-staff and a vicious death-staff combining into one that symbolizes the circle of life and death.
One handed sword
Turning bolt into the opposite, Ill go with a broad, black diamond-sword, maybe with fear inducing name leaving a red trail behind screaming whenever it is swung. Connections to cantha anyone? We could have a catana.
One-handed Axe
Something huge, light themed, double edged. golden trail, maybe connections to the dwarves.
Mace
Water-themed mace fits its defensive theme – “The great Dooboo” – a Quaggan theme would be nice.
Shield
Grand, wooden Norn shield with a totem-theme, Maybe an animal head that moves or growls at times.
Hammer
Something stupidly fabulous, with only 2 classes having access, this weapon will probably fit its sPvP-troll theme. How about “The Tooth fairy” a huge shooting star, that sprays glitter wherever it hits.
Rifle
Yet another weapon that will probably be completely deformed. Something less elegant as the predator, more barrels, more colors. How about a wooden Canthan Firework cannon?
Short Bow
This thing will make everything right that was wrong about the dreamer: Magitech with aiming barrels and multiple light going on and off, and a voice similar to the Salvage-o-matic every time you kill an opponent.
Long Bow
the “Eclipse” a bow right from mad king thorns lair, borrowed from the realm of torment, this weapon whispers and its arrows take the form of black ravens.
Pistol
Light revolver – “the punisher” sending out rays of judgement. producing a little light-explosion with every shot fired.
Dagger
“horizon” blue, cosmic dagger, crescent shaped that leaves a trail of tiny stars behind of which some are connected with thin lines.
Focus
“Celestial compass” from gw1 upgraded to the GW2 quality, the geometric forms change shape and color depending of the spell that is cast.
Warhorn
“The gathering” something festive. The Warnhorns appearance changes over the year according to the season fitting Chinese new year, Dragon Bash, Halloween and Christmas.
Torch
“Muse” A flickering brush that paints the colors into the air. (colors are slowly shifting)
Spear
A lightning spear that sends out a ray at the front and rear end.
Trident
A staff with a black hole at the end, that creates an eternal vortex
Speargun
Meh.. Ill go with something techy and compact that launches plasma arrows.
Thats one for every weapon type. Now lets see your ideas and guesses.