Name of the sword aside, I think from a game design standpoint a two handed finesse weapon could have its place in the game, but without precedent in the PHB, I am of the opinion that it should cost something. The old Exotic Weapon Proficiency feat seems to fit. If you wanted it to be biased toward elves you could do it this way, otherwise remove the elven references, and of course, call it what you like.
Elven Glaive (Exotic Melee Weapon)
This finely crafted curved sword features a long handle and a graceful design.
2d4 slashing, Finesse, Two-Handed
High Elves treat this as a martial melee weapon.
Exotic Weapon Proficiency feat
Gain +1 to Strength or Dexterity.
You gain proficiency with an exotic weapon of your choice. You can select this feat more than once, but each time you choose this feat, select a different exotic weapon.
Of course, the simpler way to do it is just stat the weapon up like you want and play with it to see if it's a problem or not. As long as everyone isn't using it, it's probably fine. I am betting we will see stuff like the above in future books, but keeping things simple has its merits too. I dislike long lists of feats and the analysis paralysis that results in character creation, and would only add something like this if I felt it was important to the setting or a particular player.
Edit: It occurs to me that backgrounds would be a good place to give Exotic Weapon proficiency