Consistent and reasonable hand luggage rules are a good idea, but the 8kg rule is not helpful. A packed 55x40x20 (or so) trolley will almost certainly weigh more than this. LH/LX have tried to enforce the 8kg limit only a few times in the past on my longhaul trips in C, but sometimes they do. I find BA's weight rule "you must be able to lift the bag into the overhead locker unaided" much more reasonable. At least 50% of my long haul trips are currently with BA, mostly because of the flat beds, but the clearer hand luggage rules are clearly a bonus.