FYI: Need a reverse speed effect for your video clips? Unfortunately, this is not possible directly within Rush, but you can run clips through the Creative Cloud App's "Quick Actions" for video. You can also use Creative Cloud Express from the browser. One of these quick actions is to reverse the video. Drag the clip into the drop zone, make choices around speed and sound, process the clip by pressing the Download button, then import the resulting clip into Rush. I have tried this, and it's straightforward to do.
Although the effect is not natively inside Rush, at least you can do what you want with an Adobe tool you can access. I hope the info helps.
You can upvote this feature request if you want to see the effect natively within Rush.