When you say SFC 4 the first thing you think of is.. SFC. Specifically SFC EaW, and OP.
If you create something totally different from SFC then it shouldn't be called SFC. You don't have to use any of the ADB rulesets, IP, Ship classes, etc. etc. You can make up your own rules, and IP specifically for this game, and still have the game play similar to SFC. Especially if you plan on using 3D movement which ADB has absolutely no license on. It will be our own IP (Except for the Paramount owned canon material) Any similarity to what ADB put out will be purely coincidental, and the burden of proof would be on them.
Excalibur has been in development for far too long, and IMO it is becoming Vaporware. Excalibur is pretty much a spiritual successor to Bridge Commander, and i don't see the people with the IP on Bridge Commander breathing down their necks with cease, and desist letters. Just as Supreme Commander is a spiritual successor to Total Annihilation. Remember, Similar to, but NOT the Same. If we keep that in mind ADB can not touch SFC 4.