Displaying a notice that a house is close to auto-demo will only result in more drama. Campers will fight each others. They'll harass owners who show up to reset the auto-demo timer. They'll harass other players who relocate to the plot after auto-demo occurs but before the relinquish timer makes the plot available to new buyers.

Just no.

You're dreaming if you think people are going to coordinate who's allow to camp what. You're dreaming if you think people are going to be okay with someone else managing to get the plot before them if they've been sitting there for days waiting for it to become available.

Owners are under no obligation to do anything with their house other than set up the estate walls and enter it once every 45 days. They aren't required to decorate it. They aren't required to redecorate it. Nor does the lack of decoration mean it never gets used. It's not up to you to be deciding how players must use the houses they have purchased.

There's a much simpler solution if you feel like you're being left out of the housing game - transfer to a server where housing is available. Bring your friends who likewise want a house but can't get one with you. Coeurl had 500 houses available, including over a dozen mediums, when I did a census last weekend. You could have one right now and it wouldn't require any messy drama-inciting system like you want to create.