I can't see BA agreeing to any sort of binding arbitration. Its simply doesn't serve their purposes.
Even a non-binding arbitration procedure will only serve a purpose if they decide to choose the nuclear option and dismiss all cabin crew and have them reapply for their position. It would show they participated in a good faith effort to obtain an acceptable settlement so that requirement gets met..but that's the only reason I can see BA sitting down at that table.
I'm relatively comfortable with BA's approach. Submit reasonable offers, stand by your words, and watch the other side disassemble.