A couple of possible solutions
- Make some classes faction independant (Bounty Hunter and Smuggler)
- Lock servers from having more characters from a faction if the balance is 3:1 or more.
- Give the underdogged faction a free medal in PvP zones.
Or just allow faction transfers free.
Or if you have a Sith Warrior at level 40, allow us to make a Jedi at level 40 immediately, without the 1-40 grind.
Any of these would go a long way towards fixing pop issues.