Please consider freezing / pausing map updates depending on a config-given threshold of online players, e.g.
freeze-threshold means that rendering of map updates pauses as long as <n+1> or more players are online.

Reason: Especially for small to very small MC servers the background rendering of maps has an impact to server performance. To handle this, admins could adjust the load of their servers.

The latest snapshot (1.6.2) already has this feature :)