After the currently planned books are released, this is what I’d like to see.
Starship Deck plans. Not tiles, but actual deckplans aimed at roleplayers. The most versatile and useful ones are 11x17 and NOT for use with minis. Yes, minis are fun and can add to the game, but deck plans for them are simply too big and you wind up with piecemeal tile sets that are great for set encounters, but frankly suck in support of a player. I have some of the old 11x17’s and lay them out during play so the players have easy access. Unless it is an alien vessel, the PC’s will already know the layout of their own ship. This transforms the game from “player make suggestion and them GM makes it upon the fly” to “player announces their intent which is then gamed out”. “All turbo shafts are down, how long will it take to get to science lab 2 on deck six” becomes “Dang, with the turbo shafts down, science lab 2 is a long way. What other options do we have?”
Starbase, Space Station and Outpost deck plans. Apparently in the Star Trek universe everyone just breath vacuum because a usable plan of a station, any kind if Trek station don’t seem to exist. I emphasize usable that can be brought to the actual table, not a black based image that is useless for actual play but looks cool on a monitor.
Threat Deck plans. Same as Starship deck plans, but for threats to make playing out boarding one easier.
Books designed to give GM Advice specific to running a game in the three main era’s. ENT, TOS or TNG/DS9.
Klingon, Romulan, and Cardassian Source Books that both add to the GM’s knowledge when handling them as threats, but also to allow the running of a campaign playing PC’s from those empires.
GM Threat books detailing civilizations such as the Gorn and the Orion. Not aimed at playing characters from them, but with information for the GM on using them as encounters.
Major Event Books. The Dominion War and so on.
Books for non-Star Fleet organizations such as the Merchant Marine, the Colonization Bureau, etc.
A book on the Frontier. The edge of Federation Space.