The idea was that links opened from a certain page would branch off that page, visually showing you how you got to where you are.
Tabs would be replaced completely with the "trail view". No more tabs means you can focus on the page you're on, without distraction. Only one page is active at a time, with exception to pages that play music.
"Focus mode" becomes the default.
The "open in new tab" functionality will be replaced with "add to queue".
Pages with active service workers in the background would be explicitly shown, maintaining transparency and trust with the user.