About your propositions @Arcurus, I am opposed to all of them this time 
you will find details on why just below.
So a 10% growth every trimester (roughly the same as 3.33% / month) means we make x10 every 8 trimesters, so 2 years. Let’s say we reach this 10% of active members once we reached 1.000 members (because obviously, the very first members of the community will actively try to make people join). So we reach 100.000 members in just 4 years. That’s what Bitcoin did, we are all good! Two years later, we reach the million, even Bitcoin can’t do this! 
So to me, your first question is off-topic. We do not need it.
About fees, we already taked about it in a different context though: Transaction fees: bug or feature?
I already answered why I am against in this topic: Certification best practices - #23 by Moul
Anti-certifications, or certifications revocation which is the same, are offensive weapons. We only need defensive ones.
edit: also wanted to comment this:
Making certification costly does not lead to honesty. It leads to power in the hands of people in function of their money supply. So the power to the richest people.