The behavior in my preset for the app switcher and emoji widgets currently involves a performance-hungry workaround with tons of duplicate widgets to give the illusion that only the scrollable container's contents are changing. However, supporting this natively with left and right-aligned button groups would eliminate all of that duplicate code and make the preset a lot easier to maintain.
Example of how the behavior works:
The normal state of the touch bar contains a scrollable container populated with various app widgets.
When the user taps the Emoji symbol, it toggles the appearance of a button group, but only in the scrollable container. When the user completes an action in the widget, or taps the Emoji button again, the button group closes.