Allow images in Comments
When creating large spreadsheets with lots of cell relationships within formulas, it may be easy to clip a small part of the screen, make annotation(s) to it and paste it in the comment that will open when hovering over the cell. This will make it much easier to understand the model
You can sort of already do this by setting the picture as the "background" of the comment. See more here: https://www.extendoffice.com/documents/excel/917-excel-insert-picture-image-in-comment.html
I'm leaving the idea active though, because this really could be easier.