I'd love to see a civilization system, actually.
Like every time you remove a block or place one, the "Civilization Level" of that chunk raises a little. Like every (100 * level²) + 100 changes raises it by 1, and monsters don't spawn within a distance of (location level - 1) chunks of any given point. So they won't spawn in a chunk with a level of 1, or in any of the eight chunks adjacent to one on level 2.
So:
Level 1 - Monsters don't spawn in chunk - 200 changes
Level 2 - Monsters don't spawn in chunk or the eight adjacent chunks - 500 changes
Level 3 - Monsters don't spawn within two chunks - 1000 changes
Level 4 - Monsters don't spawn within three chunks - 1700 changes
Level 5 (max level) - Monsters don't spawn within five chunks - 2600 changes
Obviously it wouldn't necessarily be one chunk raised to level 5, it'd usually be a few chunks of level 1-2 near each other. (though I could see a giant tower being easily 2600+ blocks and it would command a view of the now-peaceful region around it)
And maybe only changes above sea level should count as well as not preventing monsters from spawning below ground - so monsters will always spawn in caves and digging a mine isn't going to make the area any less wild.
And the 'less dangerous' monsters (probably new ones actually like wild dogs and stuff, more just dangerous animals than monsters) would spawn during the day too.
This'd make a cool addition to a civilization-based server. Along with certain blocks counting for more (like crafting benches or furnaces being worth 2 apiece, and claim flags if/when they're implemented making the area count directly as one above its actual level clamped to 5)
Poll