The 1/350 scale is very heavy these days with Japanese ships, and really, there are only a few more that I would like to see from the IJN. Currently, you can (of course!) get a Yamato or Musashi, a Ngato or Mutsu, an Ise, a Kongo, Kirishima, Haruna, and that's just the battleships. There is an Akagi, and aa Shoakaku soon to be released for carriers, the Takao class, the Mogami (in AC mode) and rumors of the Myoko class coming too. There is the Yukikaze destroyer from both Hasegawa and Tamiya, and Hasegawa has a limited release (at enormous cost!) Floatplane tender. If I had my wish for remaining Japanese subjects, it would be another common class of destroyer ('Shigure?'), a light carrier of some sort ('Zuiho' would be good!), and most importantly, a couple light cruisers.
In this line, I would recommend first a 'Agano' class light cruiser, and either 'Jintsu,' or 'Kitikami.' This last (in full torpedo mode) is a ship-type that amazingly, did little in WW2, although the Guadalcanal campaign cried out for ship of just this type!! It is a strange thing, but I have never understood why the Japanese, after cleverly creating a class of 'light cruisers' in the Mogami class, did not design a light cruiser class to take advantage of the available 6" turrets when the 'Mogamis' traded turrets for 8"... The 'Aganos' could really have benefited from the triple 6" turrets available, and would have been better ships for it (9 x 6", vs 6 x 6")
But while I would really like to see something like 'Yamashiro,' I think it may be time to have a look at some of the US and other ships of WW2. There is currently a wide range of US fleet carriers available (thanks to Trumpeter), and certainly the Iowas, North Carolinas and Massachusetts classes are well represented. But there is only one US heavy cruiser class (San Francisco 'n friends), and no light cruisers (love to see a USS Brooklyn, as fine and beautiful a class of light cruiser as ever sailed!!), plus two destroyer classes (Fletcher and Gearing), and the liberty ship (Jeremiah O'Brian).
Some British light and heavy cruisers would be a very good thing!! Some French and more Italian cruisers would be even more welcome!! And finally, a selection of more German ships (Graf Spee! Scharnhorst!!), and even perhaps a Russian WW2 ship or two would be most welcome!!