This is a service I would pay extra for. There are software such as Firstbeat Athlete that sort of does this (although workouts cannot be downloaded to device). So one would setup a training plan in Garmin Connect, as you can currently do. Then depending on how you training has progressed (how well you trained, what your training data looks like, etc.) the next week will be dynamically generated. So if the past week was too easy for you (from collected metrics) then the next week could maybe be more involving.
