Over the years, there have been a number of proposals to tag the apocrypha, as well as the LXX, and even extra-biblical books (pseudipigrapha, apocalypses, etc.). None of them has gained a lot of traction, either here at Accordance or in other groups. It could be done, though it would require expanding existing key number system(s) dramatically. The real question is exactly how many people would really use it, just as you have asked.
While everyone agrees it might be nice, Key Numbers are used most often by those without knowledge of biblical languages (or very limited knowledge). Those people's main interest is usually in the core biblical texts (OT, NT), not these other texts. Scholars tend to be interested in a wider range of texts, but the same training that has convinced them of the value of these texts has usually included courses in biblical languages. They don't need the Key Numbers.
I am pleased you've put this question out there. I'm interested in seeing just how many people respond positively.
Timothy P. Jenney, Ph. D.
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