First of all, I want to say that I know this has already been touched on (and that first one is actually my own question), but I’m not planning to turn this into a crusade if everyone still thinks the current style is sufficient; I only want to offer an argument based on the recent change for featured artists.
We currently handle remixes according to the printed credits, and oftentimes that means the original artist is named in the AC while the remixer is relegated to the title and recording relationships. In a basic data structure, I wouldn’t have a problem with this per se (though it still wouldn’t be my preference), but our database is much more powerful than file metadata, and we have recognized that in moving “feat. X” into the AC in order to take advantage of the linking and visibility that provides: the title is obviously simple text and doesn’t have any effect on artists, while relationships are not always immediately displayed (such as in the “Recordings” tab on artist pages) and are – often desirably – listed separately (only on the “Relationships” tab) from AC appearances. The combination of these means that, while the remixer is typically credited, that credit is perceived as much more minor than the original artist; of all the lists that the release/recording appears in, only one is on the remixer’s page, even for a single that should by rights appear on their front discography.
“(X remix)” is admittedly different from “feat. X” in that it could easily be considered ETI, especially if other identifying information is included: “(X dubstep mix)” for example. It is therefore likely best that it remains in the title, but that does not mean that the information should not be duplicated for the other reasons in the previous paragraph; this would also handle cases where the remix is identified by ETI that doesn’t include the remixer’s name (“Euro Cheer Mix”, though that particular one might be more a cover). While only my own speculation, it would make sense if the practice of putting both in the title stems from physical release art, where for style reasons the designer did not want to put the information on a separate line. Whether or not that is true, they can both be seen as encoding artist information rather than (solely) naming the track, and so their inclusion in the title is at times due to historical convention more than actually belonging there.
My proposal is therefore to add a style guideline for remixed tracks and remix releases modeled on that for featured artists, saying that the remixer should be added to the AC. My personal preference would be for that to be formatted as “X; orig. Y” or “X (orig. Y)”, but I recognize that others may prefer the original artist be given primary billing and wouldn’t mind switching the order and the text of either. It should be noted that whatever join phrase is used, it will only very rarely be given on official materials and so whatever we settle on is likely not going to be based on any external standard, though if something does clearly include both it is likely best to follow their formatting. Additionally, a distinction should be explicitly drawn with featured artists in that the remix designation should remain in the title as ETI.