I don't fly BA any more after they scr€w€d me twice; they don't get a third chance.
I have followed this very interesting thread though and my observations would be that BA (any any other company for that matter) can change their T & C's as often as they want. Where BA have gone totally off the rails is by not honouring the T & C's in force at the time that the booking was made. As a contract, that is what both parties have agreed to and what both should honour and I'm sure that any Small Claims Court would soon recognise that.
Let us hope that when BA do finalise their new baggage policy, they take note of this point and only apply the new rules to bookings made after the date that they are announced. Nobody will then have any grounds for complaint. If you don't like the goods on offer you look elsewhere.