Many business users complain about the fact they can not update an existing bookmark. When a bookmark needs to be updated, you have to create a new one and suppress the old one. It would be great to make this easier for them by adding an update feature to existing bookmark.
Basic feature, tens of users keep asking for this option. Keep in mind, QlikView already had this feature so migrating users are experiencing this as a step down.
This is also relevant for scenarios where the bookmark id is used, so replacing the bookmark would render all usages obsolete. Consider for example shared bookmark links, single visualization/embedded links, and (custom) extension settings that utilize the bookmark id.