I really like Firefox's current tab groups and wish that Chrome provided similar functionality. For me a better method would be to have the tab itself be the group "parent" and expand when clicked.

For example: I'm on reddit's front page. I'll open links in new tabs, then go to them later. It'd be great to have those auto-group under the parent front page tab and hide out of view until later.

Are there videos, or any screenshots of what this current implementation looks like? Like you said (and the GitHub readme explains) they don't really know what they're doing yet, but it'd be nice to see how it differs in its current state from traditional browsers, and might even convince me to give it a try.