I introduce this question with something I'll amateurishly call "Slavic sung vibrato", because I don't know of a better term. It's a sort of recognizable extendeded and pronounced vibrato that proliferates in traditional and popular sung music of the region.
Although more-typical vibrato also occurs often in the music of that region, this sounds different to me, and it also seems different from vibratos and glissandi in traditional Perso-Arabic and Carnatic music.
It is stylistic, but like other 'styles' it often seems to work in step with harmonic and melodic considerations. After listening to much music from the area over the past year and a half, it seems more subtle now but still powerful and affecting. I am guessing something of this spirit is in the 'terrible Soviet singing' Xenakis critiques at the end of this [informal interview]
(http://ada.evergreen.edu/~arunc/texts/music/xenakisFeldman.pdf) (I like Xenakis's music very much, by the way). I began to wonder, though, how this style fit within traditional Western music instrumentation and notation. In the same way the Georgian neutral third may have a harmonic function within 31-EDO or 11-limit (or maybe even 7-limit) JI - I wondered if extended vibratos might actually have some functional place in modern Western art music as more than just a simple ornamentation one day.
Sorry for the ramblings; my question is actually whether there was ever much of a known codification or notation of Slavic styles, beyond just the recording and arranging of individual folk tunes, or the writing and reviewing of new works in a 'nationalistic' style.