A few proposed new features that aims to improve the approval queue experience:
Notification upon approval
Currently, the user has no insight into the status of their pending post; they will not even know when their post is approved!
Similarly, when a post is rejected, a system generated PM could be sent with an optional reject reason.
"Pending" section on user activity page
- This section is only visible to the user him/herself.
- This section is only visible if the user had posts pending approval
- Posts awaiting approval can be deleted, but not edited.
Record full edit revisions on queued posts
This does not improve the user experience directly. However, what happens when the user finds out his/her post had been magically edited?
I actually have a PR ready for this, and it can benefit from some serious review 
"Post needs approval" Modal
Obviously, this could link to the “Pending” section mentioned above:
Additionally, what about a system generated PM similar to the one we have for Akismet? This is to empathize with the user, and it is only sent the first time that a user submitted a post pending approval.
Show pending reply in an existing topic
This should only be visible to the author:
When the user is replying to the same topic again, a composer message could be helpful:
It looks like that you already have a reply that’s pending approval:
Original reply excerpt here
Are you sure you want submit another one?
I understand that this may not be a priority for the team; I’d love to work on them once the specs are finalized.
Open to suggestions, cheers! 