Greifers seem to be the biggest problem for administrators and builders and I had a random thought last night: a definable area comprised of x,y,z points that checks the player against the defined area and disables interaction if != permission within that space.
Define the space
Let's stick with rectangular\square geometry to make the calculations easier and define an area (8 pos points would be needed to defined two sides, then the two sides connected at the corner points).

So there is a space that is defined that has an interior (within the coords) and exterior (not within the coords).
Interior Permissions
If player interacts with the world, check to see if there is a defined space. If == permissions, than allow interaction, if != permissions, deny interaction. As I type this, perhaps check player coordinates and if !=, turn off interact is the simple approach.
Exterior Permissions
Unless an area has been defined, normal permissions given on the server are allowed. Only patrol the set areas. Maybe allow inversion (only build if set).
Drawbacks
- It may be intensive to keep checking player is at x,y,z (check for permissions), I'm not sure.
- A permission set to set the permissions would be needed and it would take more admin time to set areas (though less time fixing griefed areas).
- Knowing the boundaries - some way to see the boundaries would need to be done ("/show securearea" might change the display for the viewer (owner\admin) showing the area)
- Unsure if it would need to be at the engine level or if Lua could handle this.
- Could grief from above the structure (build up and around the perimeter, then put a lava block above)
...
This is conceptual and my main intention is to foster conversation over this and maybe come up with a workable solution that would work towards corralling griefers.. Any thoughts or comments on plausibility?