They usually ask for the scan of all the passport pages held within the last 5 years when they invite you for the exam - many fellow online applicants have been asked to do so. I believe it's used to prove your physical presence status. :)
I didn't receive any notice re an interview - the only greyed out section on my application is "Citizenship Ceremony : Not started" so I'm guessing that I have to wait for an invitation at this point.
Update!
In process: Aug 17
Background verification completed: Oct 4
Test invite Oct 12, Test window: 21st of Oct to 10th of Nov
Just passed my test 20/20 (27th of Oct)
Edit: I just noticed they requested scans of all of the pages in my passports held in the past 5 years on the 19th of Oct...