In all likelihood it will never happen. Personally I wouldn't want dragonball to crossover with them anyway. It'd be guaranteed to be westernized and the last time that happened we got Dragonball Evolution. Also, I think one of the major complaints about GT was that it was too western so, yeah. Keep western influence away from dragonball please. Probably the other ones as well. They're better with just crossing over with each other. If they want, do another Marvel/DC crossover and make it canon.