Sarah, thank you for your detailed article. I am the plugin author and open for all new aspects of the plugin.

The option to select days of week is in progress.

In the article you have mentioned the idea of an indefinite option for the end time of the widget display. What about to implement that as a checkbox?
Because of technical limitations the highest and safest year number is 2037. What about instead of a checkbox a short text telling the user that he/she can give in a high number up to 2037 of year to realize "indefinite" visibility?