Ballroom,
Juggle,
Nomad and
Verger aren't really tied in with the main plot of the Third Season per se and they would just ruin the momentum. I think it's best if it goes after
Reshuffle,
Ceremony,
Domicile and
Zoetrope. That, along with the much longer
Eternal Song (the Wilhelmina-Mathilde-Merihim sidestory), would form the Shakugan no Shana S series.
It's much more organized that way. :P
These nine stories are more of a "Shakugan no Shana Gaiden" than anything else, don't you think?
EDIT: I've been working on some additional articles on the Wiki about those new four titles
Elf song has mentioned, by the way. Veeery little info as of now.
Veering away, I would like to ask the novel experts here the names of all possible locations mentioned in the anime but whose names aren't stated (like the bridge [Daitetsu Bridge] and the river where it's in [Mana River]).