Good idea, how would you prefer it in your implementation when there is no reading passage for the day? Show the forms for changing the date, hide the forms showing the date and show an editable message that there is no reading for the day, or show nothing at all?
I plan on releasing version 2.1 either tonight or tomorrow that will enable you to have this functionality plus a whole lot more! In the new version, I will enable shortcode attributes which will allow you to have more control over the formatting of the passages plus much much more.
Thank you for your compliments, look forward to hearing more comments/questions in the near future.