Thanks for the feedback and votes. This feature is in-progress.Robert Whittle commented
Please include Track Changes in Word online! I was going to buy Office 365 until I found out that I cannot redline and track changes with the online version. This is a critical feature that we use and I cannot use a version of Word without it. I spoke with several others and they said that was the single most important reason they didn't buy the web version. Please add REDLINE and TRACK CHANGES to the product!!!