But, if a Ship ate a Devil Fruit...wouldn't it just...sink?
A ship would still be affected by the Curse, supposedly. I mean, it wouldn't "kill" the ship, since ships don't have to breathe. But, it'd still be pulled underwater and wouldn't be able to "float" anymore. At least not without some sort of external propulsion. I guess a Wind Logia or Wind Dragon Zoan could provide that. But, again, supposedly, being in the water would make the ship "weaker" like we've seen with other Devil Fruit Users, and it wouldn't have the energy or stamina to actually use it's own Devil Fruit.
So, I...doubt it? I mean, I can't say it's absolutely impossible, because Oda could introduce some mechanic to make it work. But, from everything we know so far...a ship COULD it a Devil Fruit, but it'd be a very bad idea.
Just for the sake of argument, though, how COULD we make this work? Well...maybe the "black coating" on the ship actually is what protects it from the effects of the water? Maybe there's some way to coat the entire ship in Haki or with some other material, like a enhanced version of Pitch to protect the ship? This special pitch could be another substance linked to Adam Wood, perhaps? Or perhaps another form for pyrobloin to take? Similar to Seastone, but something that PROTECTS a Devil Fruit User like armor, instead of weakening them? Kind of like having a Sabaody bubble coating on the ship at all times.
https://en.wikipedia.org/wiki/Pitch_(resin)
So, I do like the idea of the ships and klaubatermann playing a bigger role in the story. But...I don't think this is going to happen. I doubt that's the way Oda's going to go with it. I could be wrong, though. And I appreciate the creativity, at least.