Great ideas Max and this is in line with various ideas that have been floating around our lunch discussions.
The primary challenge we face is that there is nothing stopping everyone from simply "referring themselves" and then using the account N levels down so they get the rebate on all of their transaction fees.
You solve this somewhat with the $20 fee to create a participating account. This fee would prevent all abuse from anyone generating less than $20 in transaction fees per year. 4000 transactions per year at $0.01 per transaction assuming 50% of fees go to the referrer.
I think the $20 fee could be seen as a pyramid scheme where the bottom of the pyramid never makes their money back. On the other hand, if you can convince just 2 people to sign up then your fee is covered. So it seems like a low enough barrier to anyone who is passionate about the concept.
Technically it is all possible.