No doubt it would be tricky mixing powders the powder bin and as you mention the left over powder would be a mix. So I doubt if mixing would be used often especially since the physical characteristics of the resulting metal can be altered by altering the electron beam itself. AM lends itself well to making lots of parts ion different sizes and shapes in one machine at the same time so hopefully waste powder is kept at a minimum.
Still it is a possibility for the future. One not possible with subtractive manufacturing unless you bolt or weld parts together.
Personally I don't think the potential of EBM will be apparent until newer faster bigger machines using some of the research of Fast EBM and other research becomes available. Using the general rules of 1) most lab research won't work real world 2) It takes 8 years lab to mass production . I may be quite a while,several years. Even though management has said t was "easy" to make machines at least 5times better.
I do think there is a good chance of a significantly improved EBM machine within a year. So I am not worried about whether present tech of EBM is used in this or that airplane part next week.
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