SFC 4 should be SFB in 3D!!
Na. While I wouldn't mind an SFC4 being more challenging as OP is, I actually liked the fact that SFC3 wasn't based on SFB as much as previous versions were. Gave the game more flexibility, and that flexibility is what allowed the gave to survive as long as it did, considering the odds against it from the beginning. That's why the mods were so fun to play. In my opinion, SFC shouldn't be as much of a carbon copy of SFB as possible.
If SFC4 were made, more races, more systems and weapons, more missions, better graphics engine, native joystick/gamepad support for 3D flight, make it multi era and allow older ships the capability to be refitted with newer tech as it becomes outdated or standardized in the fleet for modern starships.
Also, have it so that when you take on critical missions, the outcome can have a more noticeable effect on the entire map in terms of race relations, political alliances, etc., and also taking part in some classic Trek storylines would be nice.
Oh, and most importantly, larger player support!!! 6 player skirmishes isn't enough. Granted, it's fine if there's only 6 or less of you, but have a code limit of 10 or 12 players per skirmish/mission.