That locking system Ford employs on those balljoints is stupid, to say the least. it sure is a weak link, looks like it snapped right there.
Still, it was probably original and deteriorated, the new one should be better and probably not break like that.. I'd imagine there's a company out there that makes a totally redesigned front knuckle/arms to eliminate that problem.. the knuckle might even be a drop spindle to lay out more.
I dunno if that's for sure, but since minitrucking is so popular I'm just assuming.