As a reviewer, I would like to comment individual test steps (with similar experience as "comment" in Confluence provides) to let the tester know what we needs to change /improve

From UX perspective there must be an easy way how to comment specific step -> for example there is missing action/typo etc. The comment feature on the bottom (as classic Jira issues have) is not working here for the test script with tens of test steps, because you have to scroll down/up to find where is the mentioned problem and even more messy would it be when you want to reply on some specific comment. The usage is different from classic Jira Task, Story etc where the comment feature on the bottom works just fine.

Another issue would be, that the comments must be deleted when it goes for approval and I'm afraid this workaround wouldn't help here at all, user would have to manually go and delete it one by one...

Ideally I'd expect to have it on the side in the Action menu when you do a mouse hover for the step 

How would it look like, it could be then similar to Confluence. If there is added comment for some part of the text, the text would be marked with yellow background. But I think ideally it would be on XRay UX member to decide the best appearance and usability. But for sure, we do miss this feature quite a lot.