For example, engineers hope that when a user is navigating a news site, when they reach the bottom of a story, related links for other stories are embedded as portals, which the user can click and seamlessly transition to a new page. Perhaps it's not a very good description, but isn't that just a link? That sounds a lot like a link to me? So this example really doesn't make it clear to me why we need this new element…
Its a modernized ifame. It seems like they can't introduce some of these features without breaking the security features of iframes.