This is true the dialog element works quite nicely, what I wonder is can it be as extensible as a custom defined modal? with some of these approaches it's also quite easy to ensure that there are never duplicate modals open at the same time.

There's also times where you may need to stack modals ( side navigation is one that comes to mind ) but I do see what you're saying, will do some playing around and let you know my thoughts on it! :)