“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?)”
At this point, I do not believe there is any segment that will reach saturation within five years. The reason is there are so many permutations to combine digital signage with other developing fields such as virtual reality, data analytics, and other emerging technologies. I believe there is untapped exponential growth in the digital signage industry to be discovered in all segments.