Just to clarify, all this is new, not just the part about Class B seats? And why are Class B seats exempted?
Well, I voted against this proposal, but if this proposal didn't have exempted Class B, it would have been worse. Class B senators are At-large senators, and At-Large elections are made in order to let people who don't have "mainstream" views to have the chance to be elected (20% of the votes needed instead of the majority in a region). If Class B senators weren't exempted, many abuses could have happened, like for example the recall of some at large senators could have happened 2 month after having been elected.