There are other reasons than the ones he listed. For instance, one reason that the Shuttle can remain docked to the ISS without damaging the docking connector

There are other reasons than the ones he listed. For instance, one reason that the Shuttle can remain docked to the ISS without damaging the docking connector is that the two vehicles employ their respective Reaction Control Systems (RCS) to keep precisely in alignment. The Shuttle RCS is Hypergolic and has limited fuel. You would need to totally redesign the system to keep the shuttle attached to the station long term. There are lots of other reasons as well. The Shuttle was not designed to be in orbit for more than a few weeks. For a crew return vehicle, it would probably be a lot cheaper to finish up an x-38 than retrofit the Shuttle. (and cheaper still to just keep doing what we are doing now, which is use Soyuz capsules)