It's disabled on our fleet as well but I've heard that some regulators are looking at making it mandatory. I'm not sure I can see the benefit.
If the PA isn't made first then either the CIDS is disabled, the flight crew failed to complete the checklist, or they are incapacitated.
I can understand that if the EVAC command is separate from CIDS then the EVAC command is a backup form of communication but if EVAC pb sw is pressed without first giving the the PA then I suspect it might some confusion for the cabin crew. Especially in a fleet where it will take several years to retrofit the fleet and manage the multiple configurations.
Further if there are 2 means for the flight crew to initiate the EVAC then that means the cabin crew are even more unlikely to initiate one themselves and I'm not sure I like that scenario.