I counted the supporters of Estonian first III divisions. Total was 25. I did not feel like going through divIV, but I know atleast one of them has supporter. A friend of mine who started this season and I bough it for him, to motivate him to stay. Perhaps there are few more in divIV, but I doubt it. So in Estonia about 2,1% of managers have supporter.
I did some more research and counter all supporters of Spain in divI-divIV. Total was 191. It's the biggest country in BB, but might have users with more funds (real life money) available than the smaller countrys. The procentages of supporters were: 53.5% in divI-II combined, 24.6% in divIII and 8,4% in divIV. In total for those leagues have 14% supporters. If we check the procentage for all of Spain supporters was 4,3%. I did look at some leagues in divV, but found only a few new teams with supporters (free, so just joined) and rather than browse them all through, I chose a few countrys with about 330 users (so they fill 3 divisions) and found out the lower leagues had supporters 0,39% on average. So I guess we can safely say, lower leagues (V,VI) do not have many supporters in big countrys aswell. A few more countrys produced between 3,9-4,1% overall supporter coverage. I checked the USA leagues aswell, as they prolly are richer than average and have more fanatic over basketball. They had 65% coverage of divI-II and 32,81% in divIII, but the drop tendency is the same. In Japan your coverage in the top 2 leagues is 8,75% (7 teams) if we take into account only 40 users, we get 17,5% coverage. It's nearly the same as top 2 division coverage at 16,25% in Bulgaria for example.
So with about 2000 supporters (about 8000$ a month, for those who are interested how much money BB roughly makes from supporters) we can actually fill one "country" and have only one competition. Everyone else should just bugger off or play the U21 leagues? I think getting to 10k users on pay to play basis is pretty optimistic.
With browsing through a lot of countrys, I agree we need to make regional leagues, because there just is not enough competition in many countrys. It's a lot more interesting to be in a 1k manager country than be in 100 or below manager country. But I don't agree with destroying the game and making it pay to play, or play only U21. BB is not loosing that many users. It will lose a lot at the moment this change would be implemented.