“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?)”
I’m not sure any market will be fully saturated in five years, but in some ways, they all are. There is a large amount of digital signage vendors, including those who specialize in different size installations. There likely will need to be some consolidation within this sector to bring out fewer, more complete solutions. Saturation is prevented by the fact that the investment in digital signage has yet to be fully cost justified in many cases, missing many ROI elements that make it measurable. I think to get to the point of saturation, costs need to come down, metrics need to be established, and amazing content will have to be the norm. Otherwise, you have to get the price point down less than the cost of printing and shipping paper.