Very interested to see whether jesus' idea is in NGS. I think it's a great idea. Obviously we'd say artists like "Peter, Paul & Mary" is one entity, whereas collabarations like Kenny Rogers & Dolly Parton, instead of being this unique phantom entity, could instead be a one track to many artist relationship.
The style guide at time of writing this reads
"When two artists collaborate, file the track under the PrimaryArtist, and append the name of the SecondaryArtist to the TrackTitle like this "(feat. Everlast)".
I really think it is wrong to arbitrarily do it that way. One should only do it that way IF that is the way it is done on the track/release in question. There are many many times when artists are credited on an album as A & B, and it's not a choice made whimsically by the back cover art designer either, not unlike movie credits credits on works is sometimes the result of much legal negotiation etc.
And even then, we kinda know this whole "(feat." on the tracks has been happening an awful lot the last few years, and we do it in MBz because that's how they're now doing it on many releases and digital downloads, and we know it's mostly the tail wagging the dog here; that is to say there's a problem with iTunes and WMP and all those MP3 media managers treating the "artist" as different which would result in an album being scattered across different artists, so... to get around that, they make the "Primary Artist" the artist of the album (and many times quite rightly so, after all, if I am "invited" by someone to make a "guest appearance" on a work of theirs on their album then "feat." is what I could expect) and we get so many "feat." in the track title names.
Radio & TV, Record pool, broadcasting, news & journalism, we are meta-tagging television, video, audio up the ying-yang and certainly it is my experience in radio that we have all the "feat" artists replicated in the artist field/search. "Give It To Me" is listed under Timbaland many times, and under Nelly Furtado several time, and under Justin Timberlake, all for the case of Give It To Me (feat. Nelly Furtado & Justin Timberlake) by Timbaland, not to mention the (radio) and (a capella) versions of same collaboration. Certainly a meta-tagging research think tank like MetaBrainz foundation is going to want MusicBrainz to have best possible practices for meta-tagging artists to their works, whether exclusive or collaborative.
The problem is... it is downright silly to be storing and have to search track names to find instances of artists, artists should be in artists if not the main artist, when "feat." then we should still have special secondary artists relationships to handle "feat" and we should also handle outright collaboration, many artists to one track type relationships.
True collaborations, such as Kenny Rogers & Dolly Parton, Queen & David Bowie, Bruce Willis & Danny Aiello, Sinatra & Jobim, Mya & Christina & P!nk, etc, should in fact be credited correctly, and that is not to be confused with Bob Seger & the Silver Bullet Band or other "groups" that are not otherwise separate artists but rather those that are and happen to be collaborating on a a few one-offs.
Classical and Opera will certainly have divas and soloists where one would expect the credit to be Beverly Sills & the New York Philharmonic or what have you, and twenty different Beverly Sills & xxx pseudo-artists in MBz is artifice and makes it more difficult to collect and represent an artist's body of work as one, not twenty different ones.
The song "Side By Side" is performed by two people, Bruce Willis and Danny Aiello both, co-starred in the film, not Danny guest appearing on a return of the Bruno album by Bruce.
It is a real issue.
blah blah blah, this isn't anything you don't already know I'm sure, it's just... well I'm hoping you'll agree that being able to put several performers on a track should be possible, easy to accomplish, manageable if done right, and gives flexibility for finding and searching their works.
If you consider Stage, Broadway, Musicals, this is an issue... we have MBz showing the entirety of "The Music Man" all tracks credited to the composer, but really the stage, film, awards, and everywhere on the planet the song "Ya Got Trouble" is performed by Robert Preston for one, and Robert Preston & Chorus for another. Sound Of Music can be "Rogers and Hammerstein" rather than VA for the album artist sure, but most of those songs, everyone thinks, knows, would agree, are Julie Andrews and some are Julie Andrews & Christopher Plummer and some are Julie Andrews & Cast. & Cast, & Chorus could be special catch like Various Artists is.
I'd even add one more nuance and suggest it be possible to see Tom Petty as well as "Tom Petty & the Heatbreakers" works listed intermingled if one chooses to do so. That's a slightly different issue than straight-up "collaboration" but bears considering in handling. Ben Folds, Ben Folds Five? Nat King Cole, Nat King Cole Trio? Dave Brubeck, Dave Brubeck Quartet?