I'm afraid that enabling this will just make the spammy bots smarter, they could somehow check If the moderators are online or not and start doing their thing once they know they no one can stop for a certain period of time.
Fortunately,some or the other mod is always online.I'm sure the job has been divided into separate time zones.So there a mod online at every hour on bitcointalk.I might be wrong though.
It's also possible to hide your online status in your account settings too so If those can't work together, I don't see the point.
That just hides the green box besides your profile.But you can easily make out if the person is online or not by opening their profile page.
Last Active: Today at 01:34:26 PM