This function is long overdue and I am loving it. However, as someone who uses it multiple times a day, every day, I think there are a couple of things I think could make it better.
1. The ability to group files together in the same link.
I'm not a fan of "writing over" an existing file so that I can click on "update content". That is ok for small changes, but when the client is asking for significant updates/changes, I prefer to save a new file named "rev 1" or something similar. This then requires me to get a whole new link for them. It would be nice to not have to do this.
2. When I update a file, it would be cool if the viewer was automatically notified instead of me having to send another email to them with the new link (or notification that it's ready) each time. Maybe this would require the capability of emailing direct from Illustrator in order for it to work but I'm not sure. I have also tried adding the new link to the comments or just telling the client in the comments that it's ready but that doesnt seem to notify them. Which brings me to my next point.
3. When I mark a comment as "resolved" or I comment back, the client is not notified of such actions. It would be great if they got the emails the same way I do. I have clients who are both signed in a s guests and have Adobe accounts who never received notifications from me.
4. The ability to see previous versions.
I have used other proofing software that allows the viewer to be able to see a previous version and compare it to the new version. That would be super handy.
5. A space to write notes. Be that about size, colours, etc... Each artboard should have a space.

I realize that this is asking a lot of a program that is currently in beta. However, if adobe is trying to offer more to their clients, these things would be quite helpful.