"You could tag Various Artists albums with a hidden artist tag, Various Artists. You would have to do it manually, but you can do it en masse, without disturbing your existing tags, using the Tag Inspector (NOT Tag Editor, which would overwrite any currently split tags you have)."
(sorry, I don't know how to quote)
I don't really understand.. how this new hidden tag could help ? How to use it ?
An idea I have is to create a virtual tag "Artist" to use in column browser (Probably I can't use this same name ?) which would have the value ot the artist field except if total tracks in the library for the artist is < 5, then the value is "Various Artists". I can consider that when the number of tracks for an artist is > 5, even if they are singles, it's worth to show the artist in the list.
The best solution would be a splittable Album Artists field, but I've read that it isn't planned. Too complicated.