Perhaps it is not possible at this time in the development process, but I would like to suggest this feature for the future.
It would be quite convenient to be able to shut down the site, thereby preventing access to it to all users except for admins. A simple "We are conducting maintenance" type of page would appear over the duration of the shut down.
For the sake of research and sampling, you guys could take a look at how IPB implements this feature.
The great part about it that, when in "shut-down mode", every section redirects to the "undergoing maintenance" page.
Quite handy when installing upgrades, restoring files, adding mods, handling attacks, etc., as it would prevent new info from being added to the db, among other things.