Competition/technology is making flight cheaper to all and economic growth is making flight more affordable to many. Both of those are longterm trends pointing to increased demand for pilots. There aren't many longterm factors that will decrease demand. (One could imagine pilotless airplanes, major energy / enviromental crises or virtual reality teleconferencing, but those don't seem likely anytime soon.)
As for supply, the market is tight right now. (Flight schools have real problems keeping instructors.) The baby boomers start hitting 60 in four years, and the military is turning out significantly fewer pilots than in decades past. However, the "echo boom" will enter the workforce soon, and a tight market will attract plenty of people. And the airlines will do what it takes to get pilots. In the past, they have even hired single-engine private pilots! Maybe we'll see US majors extensively using ab initio programs.
So will there be a "shortage?" Depends what you mean, but in terms of pilot job opportunities, the future looks good.