They are aware of the problem, and considering a fix.

Quote Originally Posted by Naoki Yoshida
Resolving AFK Character Issues

From several users on some of our more congested Worlds, we have received requests for a feature which automatically logs out characters who are AFK for an extended period of time. We are actively looking into the implementation of such a feature, but have decided to first concentrate our efforts on increasing the number of Worlds and optimizing the Duty Finder servers.
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