The ATSB stated that the corrosion pitting caused a crack to quickly develop. It would be interesting to know what the estimates of "quickly" are. 10 flights, 100 flights etc. The carry through mustn't be very damage tolerant though this appears a one off. The break seemed to occur in the radius where the chord starts to thicken.
For a modification, what about a carbon, Kevlar or boron doubler adhered to the lower cap to strengthen it instead of metal.