Egos will keep this idea from ever happening...that, and the fact that team management will not want to risk their stars getting an injury in a "exhibilition" that means little to the regular season and playoffs.
Playing in the All Star game is ok because it's more relaxed, light on the defensive side and it is what they do on a nightly basis any way. But the pressure of playing 1 on 1 and winning will cause them to play at a pace that easily could lead to a injury that will keep them from being the best they could be for their team.
...now, a Legends 3 point shooting contest...that's what I would love to see. With a longer clock, letting them shoot all the balls at a reasonable pace, I can see where the fans would eat that up. I'm betting Larry Bird would practice all year for that contest!

Rak