Assuming that:
Caster #1 will cast matches A, C, G and I
Caster #2 will cast matches B, E and H
Caster #3 will cast matches D and F
we should be able to make it more or less in the same timespan as it usually goes for SCS, where we sometimes end up in 4 separate BO3 series streamed by one caster and still managing to end all the matches in more or less 3 hours, same as here we'll end up with 4 BO3 series for one caster as maximum, so it won't be much of a problem.
So as long as we will have 3 casters (and little to no Dunes matches :p) there will probably be no need for splitting up the matches in the first place.