SFC4 should be a ground up project - if you are going to take the time to do something of this magnitude, do it bigger and badder than anything else.
With the current state of tech, things can be done that was not possible back in the day; Improved, responsive AI - possibly one that learns (?), retro-grade maneuvering, "cruise control" speed options on hotkeys, player scripted power distribution schemes on hotkeys, larger number of weapon groups, customizable interface elements...the list is HUGE of what is possible in these times. That does not include the eye candy options possible now- larger poly models, bump maps, volumetric lighting/fog (nebula battles in thick fog), ability to randomly generate more varied terrain to skirmish around...etc....this list is also huge.
Bandwidth is also more plentiful and that should permit more players per encounter.
More players per encounter is a must have.
If more players can participate in a single encounter (within the limits of Command Rating), this will incentivize them to play more and word of mouth of the incredible times they are having in these large fleet encounters, this will naturally increase the player base.
I can only hope that the SFB roots are not abandoned...I feel very strongly that any dev would be remiss in their duty if they should forget the lesson of Craptavision SFC3.
I do understand there is legal issues with the mechanics of SFB as an IP....Deals can be made and the "setting" of the SFU as expressed in SFB can be transparently ported to a different nomenclature without loss of playability so there would be zero issue with any potential Star Trek IP claim down the road. There is already precident, Mirak=Kzin.
All things considered it really does not matter what the background of the race that built the ship you happen to be piloting, all that matters is the loadout of its systems and the skill of the pilot.