I’d like to suggest that in-line comments on documents (any maybe elsewhere) should open to the right of the document contents rather than over it and below the commented text as it does now. There are a couple of reasons for this.
First, it would avoid overlapping the text of the document, which means I can read it for context if needed. For multi-line comments I think it can also make it easier to review the referenced text and the comment thread in full.
Second, this space to the right is right now essentially empty and useless. Even once documents are able to be expanded in width I still think there should be left and right gutters for functional elements (like the comment icon itself), and so I think it makes sense to have comments show here too (if there is room).
Third, and this might almost be a feature request in itself, it might be nice to allow comments to sort of be opened/closed in the sidebar or “gutter” just like Google Docs, where you can thus scroll through the document to view comments sequentially. I’d argue GDocs’ implementation is not ideal in that long comment threads can sometimes get misaligned with or otherwise be confusing in terms of what text they refer to. But I think some kind of auto-collapse as you scroll (of previous/next threads) could resolve this. I am less concerned about this “persistent” comments view than the other two points though.