Title's a bit vague, but what I am wondering is have any of you (or your) players played two characters at the same time? In other games I have done this fairly successfully- I had a fantastic run playing a Pilot/Co-pilot pair in SWD6. Heck, when I was 10 I started playing my very first RPG (Basic D&D- red box) by playing a Wizard and a Cleric at the same time (played them for like two years or something). Now, the clear issue with doing this with third edition is the multitude of cards and such that are used in playing the game.

I might give it a shot when it is another person's turn to GM.

I've only had it done temporarily when an absent Player consented and there was a well-understood "what that PC would do" guideline.

Managing the different actions etc is no more complex than remembering all the feats etc. in another system, it's just the space requirement mostly at play.

The other issue is when there are inter-PC issues and debates about direction etc., I suggest making one PC of the two somehow "neutral, I always go with the majority, I never break a tie" etc. in outlook.