It would be lovely if MediaWiki had the option of deleting inactive accounts.
Now, this isn't really good for Wikimedia, but other corporate wikis or simply
wikis that want their user list clear maybe want to have the autodeletion of the
inactive accounts. Say that if a user hasn't accessed his account for e.g. 3
months (that could be flexible - customizable in the LocalSettings.php), the
account could be deleted, but the user (talk) pages would still be intact. So
basically, the user would have to be deleted from the database and since
deleting really active users (the ones with many edits), similar to renaming
them, isn't very safe, the autodeletion might refer only to accounts that have
~3000 edits. After that figure (or any else for that matter), the account could
become undeletable. I see some possible problems with all of this, but it
should/can be tested and I think that it might work.