I have a pragmatic concern; Stability. Many people have commented that the ships have a tendency to capsize (and some do). I roughly guest mated that using the same hull shape but ½” (12.7 mm) wider, they would be much more stable in the water.
Actually, simply extending the ship (not deepening the hull nor extending the mast heights), IMO, will help improve its stability as far as roll is concerned, assuming it comes with additional ballast for the extended length of the hull.
Because there will be more boat to take on extra weight, it will have a greater capacity to hold a larger skeloton crew and compliment than a single 3286.
I make these hypothesis based on hours of experimentation and observation of my own 3286 in the water, playing with different ballasts, ballast placement, different crew/cargo compliments/height/location on ship, and even a temporary deepened hull.
Even customizing an extended hull length using 2 3286 ships, assuming the ballast from both ships were still connected to each respective hull once combined, I believe would prove for a stable ship.
So in other words, if Playmobil did use the 3286 mould to make a longer ship ala the Unicorn, I do believe it would be at LEAST as stable as any of their current ships, if not moreso.
It's definitely feasible to make a longer ship that is also stable.
I'd love to hear if the Unicorn can float, but I doubt there is a way she can be tested with stock-masts. Extending the masts higher as in the Unicorn may likely cause it to be unstable, however, as Andy suggests.