It would be cool to see Athrun fight Rey and Kira fight Shinn. If that happens Kira and Athrun need to announce that they are the pilots of IJ and SF along with something like "Okey turn around now or regret it the rest of this war" and Kira and Athrun demolishes Destiny and Legend.

I think all three of them will share the position of Hero in Destiny. Athrun and Kira shared it in SEED. There is no reason why they all can't share it in Destiny to.