I expect that Dan's next project may be able to facilitate a true decentralized census, if it is still along the lines of his posts about basic income.
Do you want just one witness statement from each region? Also, it may be necessary to clarify some terms. What is a whale in this case, and what is an active user?
The more estimates from each place/ region the better. I will average the results.
I am being a bit vague about definitions because I don't want people to get too hung up on being wrong or right. This is a best effort basis. I will refine this post if we start getting a good feedback with some more standardised definitions.