I think that this feature already exists, at least in the capacity that I have used it.
If you double click the clip you wish to crop in the playlist tab, you will open it up into the preview pane. You can tell this is the case because the “source” tab will be selected instead of the “project” tab. With the clip selected in this way, from the playlist and not the project timeline, you can use the preview pane to seek to the section of clip to crop. You can then use the “filters” tab to add “Crop: Source” (the other crop modes will not work for this purpose) and adjust the position bars to clip the video. Again, it is critical that you are adding this filter to the source clip and not a timeline instance.
Now, before adding the clip from the playlist to the timeline and while the clip is still selected in the source viewer, select the menu item Settings > Video Mode > Automatic. Even if Automatic is already selected, this should resize the project to the resolution of the cropped source video. After this is done, the cropped video can be added to the timeline for additional editing, such as trimming.
It’s a snappy workflow once you get the hang of it. Works for me as of version 20.04.12