If they are that precise about getting everyone out of their rooms at 11:00am, they should have absolutely no problem making sure rooms are ready for a 4:00om check-in.
Depends upon how cooperative the guests are. There was a huge thread about this a few months back but IIRC there is very little the resorts can do to evict people who stay beyond the posted time. Even if a guest leaves his stuff in the room and heads to the parks, they cannot simply lock the doors and remove luggage. And there are further complications if the guest is physically in the room and refuses to leave.
What they CAN do is start charging additional fees to individuals who do not leave promptly. That would at least serve as a deterrent.
I can understand them being a little lax on the hotel side because Disney doesn't want to remove all traces of being guest-friendly. But I do think the DVC side of the business could benefit from some stricter penalties associated with late departures. Seems like a no-harm, no-foul policy if members are adhering to the guidelines to begin with.