Back in the early 70's BA converted their remaining Vanguards into Merchantman freighters. In the process they fitted a system which I think they called "STAN" which gave a readout of the weight and trim using sensors on the wheel oleos.
It wasn't used as the basic information but as a gross error check and as such proved very useful on occasions.
It is in someways surprising that thirty years later, aircraft can still take off with gross errors in weight and trim, especially since the Captain has little real chance of picking up errors in the actual loading process as opposed to errors in the paperwork.