In a second look, I saw that I rather acted without much thinking in my previous post so I renew my choices.
Just like Professor Tilley, I think that there are not enough sailing ships around for age of sail enthousiasts. But considering those excellent kits by Pyro/Lindberg, Revell, Imai, Airfix and Heller; I think their reissues would be just fine. I'd only like to have an accurate model of a Greek Trireme (preferably that of Olympias itself) in 1/144 and a 38 gun Sané designed frigate in that same scale. Just like Heller's Superbe (a Sané 74), a 38 can be built into dearth of individual ships with a little craftsmanship.
As there are two excellent pre-dreadnoughts in the shape of "english looking" Hasegawa Mikasa and "french looking" Zvezda Borodino/Orel; I drop out my wish for Tsesarevich. However, except for one or two USS Monitor kits, there virtually are not any plastic models from the age of Ironclads. My suggestion to plug this hole is the Chinese barbette ship Ting Yuen in 1/350 scale. An almost incredible thing happened in shape of a 1/1 floating replica Ting Yuen recently, and she was also a historically significant ship for her role in the battle of Yalu.
As Professor Tilley said, warships of the first world war are nearly non-existent in plastic model range. This is especially true for dreadnoughts. Except for ICM's König class, there are not any WW1 dreadnoughts in styrene. I think a Moltke/Goeben would be magnificent to accompany them and a Queen Elizabeth class with an accompanying "Splendid Cat" would be equally fine for RN fans.(Though the only one that I would buy is naturally the Goeben ). A world war I U-boat, preferably of UB-III class is equally important to represent the post-jutland German arm of decision.
The armored cruiser, a naval platform which influenced warship design so much and served in every fleet action of importance before and during WWI is totally lacking in styrene. My candidate to fill this niche is the versatile Guiseppe Garibaldi class. They were truly "best seller" weapons and were present both in battle of Santiago, Tsushima and Turco-Italian War of 1911-12 as first line warships.
As a final remark, the torpedo boat and the early destroyer, platforms which created a so deep effect in naval strategy and construction both as a result of theory and experience are nonexistent. My candidate for this class is the british "30 knotter" type TBD. With turtleback stem, low freeboard, multiple funnels and historical role (russo-japanese war), they epitomise 19th century underwater warfare.
So to sum up, I'd wish:
for "Wood and Cloth era"
1/144 Accurate Greek Trireme
1/144 38 gun Sané frigate
for "Ironclad age"
1/350 Ting Yuen barbette ship
1/350 Garibaldi class armored cruiser with multiple fit choice for different navies.
1/200 scale "30 knotter" British TBD
for "dreadnought age"
Moltke/Goeben, multiple fit Queen Elizabeth class, Lion class; all in 1/350
1/144 World War I U-boat, preferably a UB-III class.
Don't surrender the ship !