I think it should be possible to include the extracted limited opening of a page (what you see in PagePreviews) in a page using a parser function.
the syntax should be similiar to wikipediaExtracts.
For example, let's suppose you're writing an article about J.K. Rowling and you want to write a little about Harry Potter, instead of copying the start of the page, you'll just add somthing like
Main Article: '''[[Harry Potter]]'''
this will exteremly usefull when you write an article about a movie and write a paragraph about his sequel, which is not out yet, so the details might change. If you used the suggested parser function, at the moment when the sequel's article changes (maybe a little later when cache is used) so will the Preview included in the movie's article.