Brion: Perhaps you'd best begin by explaining that a "check-in" would
entail.
A ''check in'' simply means an editing session where only one edit is allowed at the same time. Its regularly used for websites with multiple developer/designers etc... and eliminates the potential problem of uploading a file that overwrites changes made by another.
A wiki implementation of this would have to be fair: It should have safeguards against page-hogging, by allowing perhaps a five minute window maximum for an edit session. It could also have session scheduling for the next editor, so someone who wishes to edit, but is blocked, can have a minute or two after the previous editor saves.. to check in to and edit that page. A simple timer, implemented as part of the interface, might be useful. The session cookie of course, would handle who's who and what's what and when is when... This is probably overkill...
Alot of this would be cause for the natural development of a client, and I understand some modest work on that is being done, though its not clear where such a client is in its dev, and what direction its taking... -SV