I think you're using your own case or two as representative. There are many expression columns that are too complex for such a scheme, and they don't follow your presumed ordering. I have some expressions which use many fields, and the order of the used fields throughout them varies to best suit the logic flow.
Here's one column:
If([AllSameSeries], <font alpha="50">Delimit(TVInfo(SeasonEpisode))<//font>[Name]Delimit(Watched(2), , / ), TVInfo(NameDisplay)Delimit(Watched(2), , / )) <font alpha="50">TVInfo(DateNoTime)</font>
Should only Name be editable? It doesn't really make sense here, since Episode, Season, Series, Number of Plays and Last Played are all indirectly related and used too.
Or this one:
[artist] \ [album] if (! isequal (firstnotempty ([conductor, 0], [orchestra, 0], [album artist, 0], empty), empty), / (firstnotempty ([conductor, 0], [orchestra , 0], [album artist, 0]) /))
Should artist, album, conductor, orchestra, and album artist all be editable from within this single column? Seems peculiar to me.
I can't think of a general purpose scheme that can be devised to make the program more useful, especially given that you can add columns to the file list, or use the Tag Action Window.
Anyway, just my thoughts.