Could be worth trying it out. Maybe a scheduled weekly post asking for missing/wanted community ideas.

I do think a stickied willing mods post with perhaps a weekly/monthly post to remind people to sign up (comment on stickied post) if they are interested and willing.

Also, if this does happen in fedigrow, you might want to update the sidebar to reflect the expanded areas of interest.

Edit: Might have found a first new community idea(small business owners).