I also agree that programming for Boomers and younger generations will be increasingly important over the next few years. For older Boomers approaching retirement age, they would probably be interested in classes that integrate both weight loss and “soft exercise” options like tai chi, gentle yoga, and flexibility. Youth fitness programs can help address the childhood obesity problem.
I also anticipate the growth of rigorous classes (both conventional & unconventional) to engage Millennials old enough to join gyms and younger Gen X’ers. Spinning, bootcamp, Tabata, and variations of HIIT could attract the active segment of these groups. Non-traditional and trendy classes like parkour could also become popular.