“Which market segment is the one that is totally saturated with digital signage five years from now? (Is there a market where the gold rush is over and every new opportunity has been already taken?)”
Five years is an eternity in technology. But I do not see any market segment being saturated yet, or five years from now. Changing technology and abilities will likely ensure that lack of saturation. I can say with certainty that the Higher Ed market will not be tapped out in five years.