This has been suggested in various other keyboard threads before. Maybe they’ll do it one day, maybe it’s complicated (logistics), maybe they think it stains the high quality of the brand.
Anyway, you can – and probably should – still add your voice in the poll thread:
I assume Purism (because they seem to act quite reasonable) will look closely how the numerous requests for German layouts will translate into sales and then decide which other layouts can be added. I guess there is a good chance for French in the next batch.