The issue isn't an issue. A person relocating is always leaving a plot behind.

If you want the ability to relocate, buy any house you can and wait for a prime location to open up

A person relocated before you could buy the house? Find out where they came from and camp that plot.

On my server we have a lot of empty houses both small and medium. If a house means so much that you can't wait, move to a less busy server.

I wish instanced housing was an option, but SE doesn't seem to be working on it.