I think a
voluntary program that rewarded people with something
other than gil for giving up one or more of their multiple plots might free up a few plots. A gil reward won't be enough, you see, since gil is easy to get and if you own multiple plots you almost certainly have more than enough of it.
I think the most enticing reward for this might be land itself. SE could open up a few more wards and then offer a pre-release trade-up deal: allow people to trade up some number of plots for a single better plot in the new ward. Three mediums for a large, for example. Or two mediums and 5 smalls for a large. Or whatever numbers seem to make sense.
And there are other rewards SE could offer: free subscription extensions, for example, or just Crysta, the captive "currency" at Mog Station. Or maybe an exclusive Ex-Slumlord glamour.
