@xzion Specifically for the pop out scenario, we include the Twitch UI to make it clear to the broadcaster that the window itself is managed by Twitch. That space also provides mechanisms for gaining access to extension details, reporting functionality and other Twitch-provided UI for Extensions to as necessary.
However, Extensions as a browser source in OBS is definitely a compelling use case and something we’ve thrown around internally. I imagine we might consider that as an option if we go down the path of enabling embeds for Extensions.