I recently tried to add another environment so I could have a true dev, staging (my gold copy of prod used for QA before promoting to prod), prod. Right now with my pro account I only have staging and prod, why could Vercel not offer additional environments at a cost of $10 extra per month? The only option now is to go to enterprise so you go from 2 environments to 12 and probably a larger price than most of us starting would accept.
I think Vercel would find this a very popular option.
Regards,
Chris