Late answer, i know, sue me.
I was thinking the exact same thing the other day, how an all-ninja team would play out, and it occured to me that there was no ninja adc. It would be a nice addition to the small Shen family, a mobile energy-based adc. Conceptually, ninjas have used a shitload of weapons, so i dont think it would be hard to figure something out that isnt a shuriken, even a shortbow would work, like you said. Smoke bombs would be fun, but perhaps, unlike Akali, you could instead throw the thing, cause instant invisibility already exists on Kaisa and Vayne, we wouldnt want more of that.
Also, for an ultimate there could be something fun like... remember Xerath's old ultimate? Where he would create those big blue blobs, with a small delay one from another? It could be something similar, only you would be blinking in them. Like, you create 3 smoke spots, and then you blink inside each one (preferably at an independent order), then after you spend like... a small time in each, you return to your original place. Think about it, it offers counterplay, like zoe, but it's kinda new, and would play out in a cool way: teamfight bursts out, you smoke-bomb 3 places. The enemies know you'll strike, but they dont know where from. You select the order (cant change on the spot, to limit your potential) on which you'll blink, and you disappear, for about 2 seconds in each. Inside the smoke you're able to move, but it's limited space, and it disolves once you attack, unlike akali. You can also get cc'ed inside too, but the point is that you can phase in and out of combat, executing enemies and using the rest of your kit to do as much damage as possible using the element of surprise. I think it's as ninja as it gets, plus it fits with the rest of ninja abilites, like 
and 
and 
(not 
, cause... what kind of ninja turns into a ball of lightning??).
For the rest of the abilities... I dont know, conceptually, ninjas have also used a lot of gadgets for disorientation, so instead of being the absolute burst (Kaisa barrage) adc, it could offer more in terms of utility, maybe a flashbang, or a poison, or both. There would also be a damaging ability cause it is, after all, an adc, so.... Maybe Ashe Q-like? You blink in your ult, throw in some empowered aa's, maybe with increased attack speed, cry havoc with a flashbang, and return back to your original place behind your frontline.
I dont know, i figure it would be pretty damn fun.
