Google introduced an option to propose new meeting times in Calendar last year that helps you reschedule when you can't make it. Since the feature is somewhat hidden (you need to click an event in Calendar to make it show up), the company has decided to make it accessible via invites in Gmail, while also introducing a deep link for note taking.
Once the functionality has rolled out to you, you'll see a new "More options" menu next to the "Yes," "Maybe," and "No" buttons in calendar invites received via Gmail. Click it, and you can choose "Propose a new time" or "Add note." Hitting either of those will take you to the corresponding section at calendar.google.com.
The feature will only be available for Gmail on the web in the beginning, and it'll first roll out to G Suite accounts over the turn of the year. Google doesn't state that the function is exclusive to its paying users, so we assume that rescheduling and note taking may come to us regular folks soon, too.