Hi Mandoss, I've received a response from Dan Holme on LinkedIn:
So STORYLINE will continue to be available to all M365 customers at no additional charge.
Then, think about the STORIES preview as two major sets of features:
CREATE: these features will be available to all M365 customers at no additional charge. You can upload or capture (record) video and images with the awesome new OneCamera which supports camera and screen recording, custom backgrounds, annotating media with text and stickers, trimming and rearranging video clips, and more… anyone can create awesome consumer-grade media content. And it’s no longer limited to your storyline—you’ll also soon be able to create video and images with these new capabilities in communities.
VISUALIZATION & PLAYBACK: in the preview, “stories” were shown in separate feeds—a stories carousel at the top of the home feed and each user’s storyline. Now, posts with video and images created with the new tools will be integrated directly into the feeds—not in a separate carousel. And again this will come to both storylines and communities, and aggregated feeds like Home. For all customers.
But for Viva customers (“premium”) we are enhancing the presentation of video and images so that their video and images are *showcased* and really stand out in feeds and expand to an immersive viewing experience.
A Viva customer’s video and images will look even more amazing to *all* users (Viva licensed or not). The premium creator can create even better looking media content.