I've just spent some time flicking between ST3 and ST4, and trying to think of any past scenarios where I thought "I wish X was visible in the song list..." and came up blank.
I wish there was a Poll option for "Nothing".
Then I thought, OK, if I HAVE to commit to some choices what would they be? Something @jaytrax said made me realise that there were 2 different scenarios that would make me come up with 2 very different answers.
If I'm in gig performance mode, I guess bpm and year might be of use. They might help us curate our set list on the fly and choose or ditch certain songs based on the crowd we find in front of us and what they have responded to earlier in the set (e.g. 80s vs 00s songs, mid-tempo vs higher tempo songs).
If I'm at home and in song maintenance mode, then being able to see options such as no. of tracks, midi file indicator, lyrics type would help me with my song "maintenance". Maybe I'm in the very long process of migrating from MIDI events in lyric sheet (ST3) to seperate MIDI file (ST4) across my 200 song catalog, being able to quickly see/filter on these fields would be really helpful. During live performance? No value in my mind.
So, 2 different scenarios... 2 different needs... both of equal value....
But, much to Peter's chagrin, I'm a big advocate for more Settings and options, so imagine if there was a Settings -> User Interface -> Song List display where you could toggle ANY of the above options (max. of 3) On/Off!!!! Wouldn't that solve everyone's different needs?