Hi Ulrich!
As it is planned, the feature is simply too intrusive. Once an article is flagged as "sighted", there is no way back. It effectively forces the community to keep on flagging, because otherwise a years-old version, that may even have been flagged erroneously, would be shown to anonymous readers instead of the current one.
If it ever takes more then 10 minutes to flag an article as "sighted" we have a problem. And that would not be a problem of the sighted version feature, it would be a problem of us not having enough people patrolling the recent changes. A lag of edits to be sighted would just be the symptom.
But I am very optimistic that there won't be any serious backlog. We have several very dedicated vandal fighters, they are the backbone of our quality control system. The sighted version feature enables them to do their work much more efficiently (no patroller needs to check an edit another person has already checked; no edits get overlooked). This might even motivate more people to engage in RC patrol because it shows them what still needs to be checked.
Kurt