Show Post list on scrollover

Sorry, No.
CMW only works with the menu items themselves, not the content of the page that any of the menu items point to. CMW does not do any checking regarding the validity of the menu items – whether a page/post/category/tag exists, or a category/tag has any relevant posts to display – it merely filters the menu items.

If you’re feeling adventurous, it’s perfectly feasible to code up a custom plugin that, for example, does an ajax call on mouseover to retrieve and show a count/list of relevant posts (some javascript and an ajax handler) … but it’s not something that I’d consider putting into CMW itself.