So, from what Ive heard in the past, a 3 faction set up seems to work well with PVP. With the addition of one more class, Bioware can accomplish this.
In the extended universe, and used by Bioware, you bring in the Gray Jedi. These are force users who feel they dont need to be sith or jedi. They will have two trees a tank and DPS tree, similar to SW. http://en.wikipedia.org/wiki/Jedi#Gray_Jedi
You then make a third faction called Independants, and dump Gray Jedi, Smugglers and BH in there.
You will then have:
Empire: SW, SI, IA
Republic: JK, JC, Troopers
Ind: Smuggler, BH, Gray Jedi
Hopefully this would make PVP more interesting at least....