Mind-dump incoming! Only do the ones you think are feasible, though I believe all of them should be doable with FFMPEG according to my experience:
Loudness normalization
You can currently set the volume between 0 and 200%, but in FFMPEG you can set the volume to target a particular loudness (such as -14LUFS). This feature exists in FFMPEG.
Audio file support
Importing an audio file should be treated as a blank video