I’ve been using Safari to play videos on my iPad due to the bug that breaks video on iOS 11. I just started it up tonight and saw the new interface which looks great.
Unfortunately, when I start playing a movie, there are a few issues. The fullscreen button which is supposed to be next to the cast button (at least it is on my laptop) is nowhere to be found, and the video doesn’t even quite take up the full page (not to mention leaving all of the Safari chrome at the top of the screen. The black bars are just me covering up tabs/bookmarks):