“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 think one segment that will be saturated in five years will be the QSR vertical. With Burger King, McDonalds, Taco Bell and other chain restaurants embracing, and more importantly investing, in digital signage combined with interactive technology in an effort to enhance the customer experience, customers will be hard pressed not to encounter signage of some sort when they get their fast food on.