Create a new right panel for the document called "Suggested Changes", which will include all changes that have not been merged into the current branch of the document.
There will be a new merge button that appears when changes have been selected. When you click it, it will merge and publish the selected changes to the current variant.
Also we may want the "Edit" button to behave like an "Edit Merge" button, allowing you to make edits on top of the selected merge. This would create a draft based on the combined version of these changes plus the current version.
The main document panel will allow users to preview the merged version, and it will highlight the changes that are being merged.