Oh, sorry Iae. I mixed up Felyn's claim of it being "borderline broken" with your incredulity and assumed you both felt the same way. Now he's saying it's worthless. (Still without seeing it. . .). Nothing to see here, move along.
As to your question, why now?
Because there is an itemization hole in actual instruments that drop. (Coda is not an instrument, it's an item with an instrument mod, just as is every other instrument mod item past the poair tambourine).
Will other instruments be released between the tiers? I don't know. You recognize it has to be balanced it without making it overpowered for kiting bards, which is what your initial concern seemed to be. There's also the problem that real instruments are terribly specialized and will rot after the first time they drop, so not all players are wild about them being on a loot table. Also, other instruments (non-percussion) are dodgy at best, due to the fact that so many of our songs are completely unmodified by instruments.
In any case, I'm pleased at the chance to diversify my dps abilities. Much like I'd advocate more high damage high delay piercers (18 and 19 damage? o gosh!) for those rogues that like high BS numbers (that do the same dps as low damage low delay piercers in the same tier), I'd love to see a lot more more actual instrument itemization. Diversity is fun.
Although first, I would like to see more songs affected by instrument mods >=(.
P.S. Don't do it Regasin!