If I understand correctly you want calibre to hide a column name in the tag browser if no values are being shown for that column. This can happen whether or not a VL is applied.
I would be nervous making this the default behavior. I can see no end of bug reports saying that "precious column A" disappeared from the tag browser. I will think about whether or not it could be an option. (What I mean by that is that I will ask Kovid if he is OK with it.
). The bug reports will arrive even if it is optional, albeit fewer of them. There are also possible interactions with Kovid's new content server work.