I wanted to provide a quick update on this request. An all-new rich editor for creating and edit descriptions and comments are available for the new issue experience in Jira Cloud with the new Jira issue view. If you open an issue from your board or backlog that has the new issue view enabled, you should be able to see it for yourself.
The new experience is available for everyone using Jira Core and for some % of Jira Software and Jira Service Desk customers, we're progressively rolling out the new experience to the rest of Jira Software and Jira Service Desk customers.
If you're using Jira Software Cloud and you still don't see the new issue experience, you can turn it on/off in your user profile under Labs.