Advanced Sharing w/ Markup Collaboration

We are about to start working on a 3-part release that includes teams (for all accounts), commenting w/ @mentions (https://bit.ly/3MYN5L7), and annotation on shared markups. The third piece is pretty special. Currently when sharing a markup, the recipient must "duplicate" in order to add annotations. This creates an entirely new document and the original sender cannot see or edit and only has the option to "duplicate" again if shared back to them. It's not efficient and really not collaborative. Our plan is to allow all recipients of a shared link to add their own annotations. This will not be in real-time like a few other tools offer, instead, we will incorporate a "layering" model similar to design tools like Photoshop or Figma so users can show/hide the markup from each collaborator. The original creator will maintain ownership, but anyone with the share link can enter an email (full account creation will not be required) and add comments and/or add markup on their own layer. We think this will be quite transformational for collaboration and like nothing we've seen with any screenshot and annotation tool on the market today.