Adc's always think they need buffs. Most of them honestly don't. A few like ashe don't get nearly as much - with the champs and items these days - out of their kit's utility focus as they should and maybe deserve a bit of love. But if anything adc's need some re-tuning.
They either get 1-shot, or they don't and can then dps down anyone and remain out of arm's reach of any melee that jumped on them if they get even 1 sec of peeling due to crit giving them higher in-combat movespeed than melee's have and melee's having already used their gapcloser to get to the adc.
What adc's need is less powerful crit damage. No... hear me out adc's before you throw me to the stake and burn me. Less powerful crit means you don't have to rush 3+ crit items every match. Which means more room/flexibility to get a ga, a maw, or a lifesteal item earlier in your build. Which means more options to deal with enemies jumping on you. Combo that with returning melee's their rightful superior in-combat movespeed and you now have a strategic battle between melee and adc rather than a battle that is either a melee 1-shotting you with no counterplay or you not getting 1-shot and nearly-inevitably killing said melee before they ever have a fair chance of catching you again (due to their gapcloser being on cd until after they're killed). That's what adc's really need. Moreover, it would help diversify adc's because it wouldn't favor a certain group of adc's over the rest. You buff crit? Well now stuff like cait starts taking over. You buff bork? Vayne, lucian, etc. You make it more equally viable to have all sorts of 3 core item build rushes for adc's rather than just bork+cleaver+zeal item or stormrazor, rapidfire, ie etc. then you make it better for ALL adc's... not just ones that rush the 3 items fitting the build path that is buffed in a certain patch.
There's a lot of other stuff to change too. Targeting certain overpowered bruisers and fighters, making tanks about cc and durability again while reducing their offensive power - especially sion. Things like that.