There should be a way to send an email asking somebody to input something. This input could be used as dynamic content. It would be nice to allow a user to change a variable. For example, asking a user what time something should be or giving the option to change a time. It would also be nice if there was a comment box for email with options. Personally, that would solve my issues, but I feel like a general "Ask user for input" could be more valuable for its wide variety of uses.
The recommended way to do this is to use approval flows. These can receive input from users and then proceed based on the selected input.