Well, I think instruments will have a role in the game as posted right here on this web site under Class Descriptions ....
There will be some songs that require instruments, but the intent isn't to force bards into swapping weapons and instruments back and forth all the time to be effective. There will likely be animations for bards to play their instruments in social settings, but it's not yet certain whether that will be in place at the time we launch or if they will be added in the future. Bards as well as all bard sub-classes play music as a form of spellcasting during combat. There are no plan for them to play music for entertainment purposes in game.
I played a 70 bard in EQ1 and now play a Troubadour Bard in EQ2. I suspect it will be kinda the same as EQ1 where the instruments have modifiers that will increase the strength of the song; at least I hope so. Hope this helps clear things up.