Think I said this somewhere, but can't seem to find where...
"Condemned" (or however it's spelled in game) has nothing to do with the size of the plot. It means that the plot is not owned by someone with an active subscription. Any plot that was unowned on all three shards was one that could possibly removed from the world, regardless of size, in order to allow for the revamp. In some cases, a plot larger than 1600 sq. m. was deleted because it allowed other plots that were too small but owned to be enlarged, or allowed more plots around it to be enlarged. It totally was a case by case basis.
The only plots which were completely safe from deletion are those which were owned by someone with an active subscription. If you want to do some "pre-planning" of what you want to purchase, in fact, you could go to your favorite community, look at what is condemned, and know that those plots will soon be available for auction (assuming you are not in a guild community when you look, of course).