“Does gesture control really have a place in digital signage, or is it a flash-in-the-pan trend?”
I believe gesture control is here to stay for some sets of digital signage. As gesture control continues to improve, it could become a more mainstream way to interact with displays on par with touchscreens. Gesture control is seen as a more fun way to interact with digital displays because it lends itself to campaigns that use gamification and fun interaction as their selling point. Gesture control can also separate the control of the screen from the screen itself so that interaction with larger screens and/or screens that are not immediately in front of the user can be controlled.
Gesture control will have long-term uses that are different from what touch enables and will continue to prove itself useful in certain applications for years to come. It may never overtake touchscreens, but will continue to improve and be more ubiquitous over the coming years.