This allows the following cool "editprotected" flow:
- Requester puts the modified version of the requested page somewhere else (maybe a subpage of talk page).
- Requester tells admins revision ids of the modified version and the original revision which the modified one is based on, possibly with a gadget.
- An admin edits the page with &undoafter=<modified revid>&undo=<original revid>.
- If there's a conflict, admins can check &diff=<modified revid>&oldid=<original revid> and manually apply that, or ask the requester to submit a new "patch".
Actually existing code can work in this way, and it's only some sanity check which blocks that. gerrit 91943 is a demonstration of removal of that.