I've never heard of aluminum spokes, and I certainly wouldn't recommend aluminum as a spoke material except as as disposable item for extreme competition.
Ductility is not the issue at all, to be sure. The issue is fatigue strength. The concepts are difficult to impart, outside of a university level materials curriculum. What is needed for spokes is both very high yield strength, and high fatigue strength, which tend to go together. Piano wire, and springs of all types, have the same requirements. I.e. the ability to withstand stretching elastically over a very large number of cycles. "Stretching elastically" means returning to the same original length when the stress is removed. "Withstand" means without fracturing due to fatigue, i.e. after N+1 cycles.