Yes TPE4 is processed by v17 and stored as the "remixer" with the content taken as the name of an individual or other entity e.g. a group.
This means that there will be a row in the artist table for this "artist" (= person or group that contributed to the recording in some way, could be the title artist or composer, remixer, orchestra, producer, cello player etc.), and rows in the songartist table that also has strArtist field denormalised for debug purposes.
I think it is wise
It allows for all those title artists that also do something else (compose, produce, mix, play drums or sing backing vocals) on other songs by other title artists. There is a whole world of discovery possible with fully tagged music, finding the songs where artists did other things, or all those produced by the same person etc. It does mean that the artist
table contains not only title song and album artists but any one (inc groups such as bands, orchestras and choirs) that contributes in some way to recorded music. When Kodi displays the artists node it only lists those that are album or song title artists, under roles such as remixer it shows those that contribute that role.
In your example "Wendy And Lisa Slow Jam Mix" is a combination of the name (names?) of the remixer(s) and a description of the kind of mix. Say that "Wendy And Lisa" is a single entity i.e. you don't want "Wendy" separate from "Lisa", then I would propose that TPE4 should be set as "Wendy And Lisa", with "Slow Jam Mix" belonging in either the track title, COMM (comments) tag or TIT3 (subtitle) tag. Kodi does not process TIT3 yet but it is on my list.
That make sense? Questions are welcome, but if you are looking under the hood of Kodi at the db then expect a technical reply. When I added the extra tag processing in v17 I only had the written ID3 standards to go on, and yet to find out what people have done with their tags in the wild. I believe this treatment of TPE4 is the most useful and flexible one.
