If you are interested in WWDC, you can use this app to watch live. No developer membership needed. (You can also watch on an Apple TV 3 or 4).
You can also watch the last several years of sessions – with a searchable transcript that is synchronized with the video!! I assume no transcript for this weeks live sessions, of course.
I’m really curious about that as well. So far I haven’t seen enough to know one way or the other. I don’t think you’ll be able to mix different types of tabs in one window, for example data sheet, forms and procedures. If that IS allowed, it would have to change the toolbar when you click on different tabs.