Eh, I don't know about keeping the same races and adding a couple new ones. I feel like they'd just split it up much like how Goa did with E4X where the factions are no longer just called rebels, but are more fleshed out and differentiated. My personal take on it:
TEC: formerly the TEC Loyalists, they rely on the wealth of the central worlds, having become something of a corporatocracy and a walled garden.
Human Federation: formerly TEC Rebels that have become even more open to allying themselves with the darker elements of humanity as they proceed ever further down the path of destruction, giving their units more range
Orthodox Advent: previously Advent Loyalists, the OA will go even further down the path of culture, allowing them to become so proficient as planet-produced culture that they cease constructing Temples of Communion altogether. To deal with their war with their brethren, they have developed shield-weakening Ion weapons.
Purified Unity: previously Advent Rebels, the PU will focus on ascendance more than anything and replacing many of their weapons with psionic surge batteries of Psintegrates.
Dark Fleet: formerly the VL, the Dark Fleet have become ever more paranoid and have been compelled to bring the collateral-damage-causing Phase Cannons online for more ships than just the Vorastra due to TEC and Advent resistance to PMs, giving them guaranteed damage directly to enemy hulls. Kosturas have also been enhanced.
Exodus Fleet: a merger of VR, AR, and TL results in an alliance that can field a very diverse unit set and is able to bring together many of the best features of each race. They begin naturally very weak and with poor access to culture but can eventually grow into the most powerful faction through research.
I feel like that covers the basics of the currently-playable factions. Outside of that, just add in a new faction for the Vasari's Darkness. Each of the above factions would also get a couple new capital ships and swap out/add some frigates. I guess if we needed another new race in addition to the Darkness, we could always bring in the creators of the PJIs (unless they are the Darkness)
Further, research should be expanded to have 12 tiers instead of just 8 and I'd like to see some way of reducing fleet capacity.
This is of course in addition to the necessary improvements to the engine and MP. Also, even if we don't get a campaign out of the box, at least give modders the tools to do it.
my more complete thoughts: http://pastebin.com/SCLzDMZU