When having multiple AjaxLazyLoadPanels on your page, they all block their Wicket request thread until the content is ready to load. This can be problematic when you try to wait for some background job to finish and want to poll for that job to be ready, and only then update the contents.
The improvement would be to add a method that gives the developer the option to not update just yet (isReadyForReplacement) and when it returns true, start the replacement. By default this would return true, implementing the current behavior of the AjaxLazyLoadPanel.
Furthermore to improve the responsiveness of the ALLP it should add a single timer to the page that can be used by multiple ALLPs to update themselves. The timer would poll each second and the ALLPs would use Wicket's event bus to update themselves. With some reference counting, the timer can remove itself from the page when all ALLPs have updated themselves.
This enables refreshing the page as well when outside an AJAX context, or having a user be impatient and pressing F5.