As seen at the end of the FF14 Trailer (TGS 2010), the characters mention giving the Bard something to sing about.

Would we ever obtain an ability to allow Bards to freely play their Harp?

If it was done as a Skill, it could be unlocked through a set of Quests (like the Item Dye or Materia skills), becoming accessible after obtaining the Bard Job, allowing the Player to play notes with their Weapon/String instrument real-time via a single button press; similar to playing the Ocarina in Legend of Zelda: Ocarina of Time.

Alternatively, an obtainable set of Emotes for Bards to use to play a Single note, such as "/note_c#" for a C Sharp Animation and Sound, allowing the player to use Macros to chain notes together.