This 5 year old study ( www.skybrary.aero/bookshelf/books/1149.pdf
) concludes that such systems might not provide the accuracy needed. I agree that for GA the cost of the system would be prohibitive. However, for Commercial, Cargo and Business aircraft costing from $1 to 10's of millions, the cost sould be more manageable. The referenced study above used 1700 W&B incidents in the past 40 years. The cost of destroyed aircraft is massive; the cost of human lives in incalculable. I'm sure that a dedicated research and development program could produce an accurate system.