Thought: how viable would it be to pad print the secondary legends, similar to how some of the Cyrillic sets have been done (I think?).
I actually know very little about the process, so it may be that it's not viable at all (plus I know pad printing is somewhat frowned on, since it's much more susceptible to wear).
That said, I think that just a normal set with the suggested colors could be interesting, even without the secondary legends. I think people are just interested in the idea of the kana because it adds a cool bit of flair.