Im assuming AT doesnt have a concept of periodization outside of what is defined by plan builders phases and it doesnt have an idea of a users goals outside of the high level plan a user chooses. What if a user could specify a difficulty default for each zone (productive by default) so that if they wanted stop progress on a zone but still hit it regularly to focus on another zone. say you are in offseason base 2, but you dont want to crush threshold and you want to aggressively do endurance. perhaps you could even choose recovery to replace a type with z2 or z1. you can do this manually, but this could allow folks to tailor their plans more. could still be overridden by AT if it detected you were struggling.
or maybe by day of the week so you could hit it hard on thursday, but easier on sat.