I think you may be taking an overly prescriptive view of what’s written in the SOP. Our manual says to turn the speaker on to do the oxygen check. It doesn’t say to turn it back off. I don’t take that to mean we have to fly with the speaker on.
I agree that “nothing’s happened yet” is by itself not necessarily a solid argument, but coupled with the facts that Airbus hasn’t listed a specific limitation against it, I think it’s fine.
I’m willing to reverse my stance if there’s any technical word from Airbus against doing so though.