If the imported video (for whatever reason) is not the correct rotation (eg: upside down) allow the user, perhaps in the View menu or Preferences, to rotate the video until the correct rotation is achieved.
This will make editing the video much easier as I have found editing whilst the video is upside down is not as easy to do.
At times video I use is not the correct rotation, I use either Exiftool or FFmpeg to apply the metadata -rotate flag to correct this then edit/join in Avidemux. As I've read on this forum your not looking to support 'auto' rotation based on this metadata tag when a video is imported so perhaps you could incorporate my above idea?
After editing I know I can save out my video using MP4 Muxer which now has a rotate video setting.