Do you have very many real world examples in your library where the Peak Level (R128) doesn't have enough headroom to adjust for Volume Level (R128)? In my library of 6400 audio tracks I found just three and it only made a 1.6 dB or less difference. I also would never play back those tracks without the entire album so it wouldn't matter anyway. The one needing the most Volume Level (R128) measures 15.8 and it has a Peak Level (R128) of -15.1 dBTP. The actual adjustment is 14.1 dB.
As I mentioned before, only 1% of the music I have analyzed so far (151/~16,000) requires more headroom than -23 LUFS provides; and most of those tracks are classical music, which would generally be played back as albums anyway. I think -23 LUFS is a very good target level for music.
Vocalpoint suggested that the target be raised to -15 LUFS though - only 38% of my library would be able to be properly normalized using that as a target level.
I think if people are finding that playback is too quiet when using Volume Leveling, the solution is to use it in conjunction with Adaptive Volume set to Peak Level Normalize, rather than raise the target level. This will ensure the current playlist is level, but plays it as loud as possible while avoiding clipping.
For videos, however, more than 50% of my library requires more headroom than -23 LUFS provides. The worst offender is a film which requires 11.9dB of additional headroom.
Overall, it seems that -30 LUFS would be a suitable target for
most films though. I'm not suggesting that the default be changed, but I would like some way of adjusting it. (and using Internal Volume seems like the neatest solution)
But that doesn't tell the whole story - when you downmix to stereo, the peak and average levels can change quite a bit. Some files require additional headroom, and others don't need nearly as much.
Matt has tried a few ways of estimating it, but perceptually, I don't think it works very well for films. It seems to do a better job with music, mostly being ±3dB with the files I have tested so far.
I think the only real solution is to have an option that will also analyze the downmix. There are reasons why it's not a good idea to do this, but I can't come up with a better solution.
But it could also be argued that volume leveling is not as much of a concern for film playback, because they're going to be at least 90 minutes long, and it's not as common to be playing them back-to-back.
It's mostly a problem for videos that have been created for the web (YouTube etc.) which are stereo, but simply need more headroom.