Performance: AJAX Move Sitemap: AJAX the LockRegistry.isAcquireable method as it is very slow

Checking for the performance of the AJAX sitemap engine when trying to move a page (online demo test web site with 40 pages in 2 land - so on a small web site), and most of the time is spent in the LockRegistry.isAcquireable methods in order to check if all pages could be moved.

1) It does not look like this check is really used as I tried to open an engine with siteadmin (while trying to move the page with root in another brwoser) and nothing prevents me of moving this page.
2) if we verify the locks at the opening of the sitemap (and for all the pages) this is probably not the right time in order to perfom such checks, as a user could perfectly steal a lock on another page during the time you find and select the page you want to move. So perhaps we could AJAX the check of locks and, in the case of selecting a page to move, only check the lock of the page and sub-elements once the author selects the page he want to move (= only when he clicks on the radio button).