So infinite arrows/ammunition...

[Tharian]

what would they do? The shield that Gladiator's/Paladin's, Thaumaturges/Black Mages, and Conjurers/White Mages can use has a primary effect of increasing Block Strength and Rate. Without a Shield there is absolutely no possibility to block an attack. So again, what would they do? I doubt it would make sense in any way to have them increase the damage potential that an Archer/Bard is capable of dishing out, otherwise the Archer/Bard would potentially out DPS the other DPS classes, at least unless the weapons that the Bard already has access to somehow got nerfed when the ammunition was introduced? So that raises the question of what effect these ammunition slots could potentially have that we as Bards do not already have access to. And if they are an infinite use item, instead of a consumable item, then that raises the question of will there be a Relic Ammunition?

The problem with adding a "arrow" or "quiver" offhand is no matter what stats or "additonal effects" they put on them, eventually one or two of them will be deemed "The Best" and be overpriced and the rest will be Market Board Floatsam. on top of that, Why add more gear bloat when they could just as easily tack any of these things on to new bows, and not have to try and balance classes around a main hand and off hand that isn't needed....Also "Stat Sticks" suck.

If like the OP proposes, and the ammunition item is an infinite use item much like a shield currently is. Then this point of view, that one will be deemed the "Best" and thus will be over-priced, is a non-starter argument. The reason I say this is because they would be handled the exact same way as Shields currently are. With one Ammunition being the Relic Ammunition, and another being the item level 115 ammunition dropped in Coil. It just wouldn't make sense for them to do it the way you are suggesting and have them all be purchasable on the market board if they are planning on making them infinite use.

Of course this entire line of arguing assumes there are even plans to make an ammunition slot item.