It would appear they are also setting the stage for major changes to their Faithful and Discreet Slave Parable interpretation in the future.
By including the Faithful & Discreet Slave and calling it "an illustration" in the very same Watchtower where they say they are doing away with interpreting illustrations as types and antitypes, the Society is preparing in case they need to update this teaching in a major way.
Also, the Society now claims they will no longer interpret Parables as applying to certain classes. They already started this with removing the Evil Slave Class.
But, if the Evil Slave is absolutely not a composite class, then why would the Good Slave be a composite class?
Looks to me like they are getting ready to declare that the Faithful Slave was just a parable "warning his spiritual brothers about what
would happen if they lost their sense of vigilance and did not prove to
be prepared," which is what that quote above explains.