Unfortunately it seems that Microsoft has decided that they will no longer support the feature and has announced that they will be shutting it down. According to Microsoft, “Given the service relies on providing you with new and exciting content regularly, Microsoft has given much consideration to the reality updating the service regularly in order to sustain it. Therefore, the decision has been made to scale back our support for Xbox Fitness over the next year.”
They also add, “Beginning today, June 27, 2016, Xbox Fitness content will no longer be available for purchase. For existing users of Xbox Fitness, the content you’ve purchased will be available to play for a year, through June 30, 2017.” What this means is that if you already own Xbox Fitness, you’ll be able to keep using it until next year, but if you haven’t purchased it yet, you won’t be able to.
Based on the comments on Microsoft’s blog, it seems that many gamers aren’t too thrilled about it, especially some who have just bought it and who basically paid $60 just to use it for a year. There are also some who are upset because this is a reason why they bought the Kinect accessory as well, but either way it looks like Microsoft’s decision is final.