If they're participating in the health care exchanges, they have a very limited set of criteria they can use to set pricing on the exchange (I believe it's just age and smoking status; sex is now a prohibited criteria, as are pre-existing conditions). I don't know if employer based healthcare can charge differential pricing based on whatever.
AFAIK, the fitness programs were based around many large employers running their healthcare insurance on a self-insured basis (often with an insurance company handling adminstration of the plan), and there's an expectation that increased fitness will decrease costs. Since the employer is paying the actual costs, decreasing them shows up in the bottom line; and incentivizing employees to do the fitness program might make sense. OTOH, some sort of requirement to wear a device to set an employee's healthcare premium sounds invasive, but I dunno.
Unless it starts to cost them money, they won't inovate. If they for example start to be limited of denying coverage, they have to bring their customers to live more healthy. Currently denying coverage is an gold mine for us insurers.
I'm not sure if statistically modelling risks really works. If one thing doesn't get you, then something else does. For instance they still say exercise is good for your heart but if you train for two hours a day you are at risk for A-Fib
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5135187/
For one thing many health risks take 20+ years to develop but you usually contract for health insurance for a year. By the time a health risk develops you will probably be with another insurance company, or your health insurance company will have been bought by another insurance company and then bought again and then bought again.