Problems in metadata taging with Classical music

Is it imposible to support more metadata fields? I'm a lover of classical music and currently the songbird has the same problem as iTunes (or allmost any other aplication...). It would be great to find editable fields for: Orchestra/ensemble etc, conductor, solists (multiple would be great!), opus number, year of composition (in adition to year of recording/album release), etc etc...

I understand that some metadata formats (like ID3) are restricted and there are limited number of fields to use. But Orbis Comment for example should be unlimited?