Legendary with ascended stat
Slightly confusing question. I personally imagine that Legendary will get a bump up to Legendary stats as Ascended is suppose to be the step inbetween Exotic and Legendary. I seriously doubt the Legendary skins would change as that would pivve off a lot of people who put tons of hours into getting that Legendary for its looks.
Arenanet has stated that Legendary weapons will ALWAYS have the best stats in the game, and that they will Match the highest stat tier beneath them.
As such, when Ascended Weapons are released, Legendary Weapons will have their stats improved to match those of Ascended weapons.
Legendary Weapons should never have better stats than other gear that is easier to obtain (Currently exotics, later Ascended)
They have not said anything about changing Legendary skins. It’s possible, but I find it highly unlikely. The best we’re liable to see are bug fixes should a legendary’s particles not be legendary enough.