The same team that builds Visual Studio Online also builds Live Share, and so we care very deeply about collaboration. That said, you can spin up a new environment for a PR and then start a Live Share session from there. This allows others on the team to jump in, and leave comments, entirely asynchronously, and without requiring a specific “host” to be online.
We have a lot more to do in order to make this scenario truly shine, but we’re very excited about the possibilities moving forward. I’d love to hear more about your specific thoughts on PR reviews, and what kind of workflow your team would find compelling.