i would like to clarify on the doubts that everyone is having after recieving the email.
i got in touch with cic agent after being on hold for 1.5 hours. They clearly said that it depends where is your application status and which process is being undertaken at this point of time.
For instance for applicants who are on their final stage of background check, it will show an estimate of how long will it take to process with an ETA of time when would their be a decision on their application.
The agent was not providing clear information about how the progress bar will look like and how it will show the current information but made clear that not every applicant will have that bar on 12th Dec and some might have to wait for a while to get that update which depends on their server.
I think this is a great step taken by IRCC to show an applicant where their application process is at current stage.
I hope it helps