I think dogs/wolves that you can tame or find in the wild should be able to eat peanut butter. Dogs really enjoy peanut butter in the real world so I think it would be a nice addition for the next or future farming update. Thanks for reading. Looking forward to the Italian update coming in the near future!
With the current technical possibilities, this would not be possible, as we cannot modify what items you can use to "feed" (breed) the dog with since it is a vanilla mob.
I will still leave this suggestion here for voting though in case it ever becomes possible. 😀