You know who will defeat Goldberg? The one man that ended his streak long ago in WCW; Kevin Nash. AND THEN, Joe will defeat Kevin Nash for the TNA Championship after a mentor/student rivalry ordeal and Joe will be on top, AGAIN. It works, see?
I'm only kidding, but I like Goldberg. Still, I can see where the concern is, as his gimmick and resume really don't allow him to lose, per se, and when people see an undefeated streak, they get worried the guy who beats him is going to bury his credibility. It's something to consider, though.