I agree that is certainly a very interesting rule. It makes a lot of sense from the customer's standpoint, and if properly implemented, probably saves everyone a lot of hassle and time at check-in by avoiding arguments from customers who packed based on their expectation of the "most significant carrier's" rules (and cuts down on customer service complaints and refund requests afterwards). Particularly in cases where it is the "most significant carrier" that actually sold you the ticket, and whose rules you are most likely to look up. But I also agree it seems like a challenge to implement, unless perhaps the LH has automated this in their system, to show an agent exactly what amount of luggage a particular passenger is allowed based on their itinerary. More power to them if they are able to do it!