[abeppu]

I think the hard part is knowing which routine will be appropriate and effective for a given person. What's their existing fitness level/experience? Do they use a gym and if so, what equipment do they have? What are their goals? What's their injury history?

And while adding a likes/ratings/whatever system might be helpful, I'd much rather see a system that considers actual information about people's progress. Did you get stronger? Leaner? Did your mile time improve? Did you get bigger delts? At a high level, for a given goal, routine selection is a contextual bandit problem, but so far as I can tell no one treats it that way.