Bram's diamond

Bram's diamond just caught my interest. I recently had a premiere of an a capella
work called Vedic Mass written for two sopranos and two mezzo-sopranos. The work is
based on this very same 7-limit diamond which I've notated in standard notation.
For rehearsals leading up to the premiere, the singers - a Sydney-based group
called Voiceworks - trained using a Csound crib in 12-tet. It was my hope that with
the harmonic bias of the dominant 7ths & half dimished chords, the vocalists'
intonation would gravitate in an a capella situation towards 7-limit JI. However
even though most aspects of their performance went off beautifully, I found, given
the degree of vibrato, it was hard to tell whether vocalists actually sang in
7-limit JI. When the piece is done again in easter next year the same singers will
be directed by a more experienced musical director who wants to train the singers
using a Csound crib in 7-limit JI. Some singers, like Jane Manning, argue that
vibrato is their way of dealing with fatigue. Is it too silly to expect that such a
work will be realised in 7-limit JI by operatically trained singers given their
irresistible inclination for vibrato ?