a "select all" option in item view
Edit Added on May 12 17:28
I think you have put it in the wrong section then, it needs to be in view list or collections. Let me know which one and I will move it.
I think what you're describing already exists in Collections view--you just use the checkboxes to 'select all,' and use the appropriate drop-down lists at the bottom of the page, though an additional 'check all'/'select all' link could be added. The checkbox functionality just needs to be transferred over to View list as well.