For example, using the draw.io plugin for Atlassian, customer would like to add diagrams to the Jira issue's Description field. Currently, this is not possible because of the cloud API's limitations. 

Ideally, customer would like to be able to add/embed diagrams in the Description field, so that the review flow is more intuitive. Besides, it will make the documentation export easier (i.e., diagram can be shown in the exported document's description albeit not editable)

FYI: Alternative from draw.io described here where the diagram can be attached as an attachment.
https://www.drawio.com/doc/drawio-jira-cloud