Still doesn't sound right though and that line doesn't appear on BA News Interactive or in the article on the front of the latest BA News, so it does make me wonder. I've checked in LOS with trolley bags over 20Kgs being passed off as handluggage, so it can be done. If I hadn't weighed the bags, we would never have known. I've also crewed plenty of LOS with all sorts of things being brought on board, including engine parts.
If you're right and it IS going to be 23Kgs, that actually might save some time in the terminal but I'm really surprised the unions have agreed.