Thematic issue in lol. Musings on the system by which AD carries do damage.
It doesn't make sense to have the number of swords in your backpack impact the damage dealt by a shotgun shell.
Too lazy to type up a wall of text about it, but wouldn't it make more sense to have marksmen buy ammunition from the shop and swap it out when they want to use it? (ex, if they want lifesteal, use vampyric rounds. if they want a shiv proc, lightning rounds. If they want to use frozen mallet, frosted rounds. If they want Blade of the ruined kind passive, use Ruined rounds, etc). Obviously, they would have some kind of low level ammunition to use early game or against minions.
It could lead to some cool shit going down, give even simple champions like Cait another layer of complexity. Hell, you could introduce some free item into the shop to let any ranged champion use these, to keep those hipster ad carry leblanc players in business.