It would be 100% SP because each account requires a minimum amount of SP to be created. If they're a new "temporary" account - they wouldn't be able to depend on those funds for an emergency. It's a limitation people would have to live with.

And it absolutely is a system where you have to achieve a certain level to get rewards. The bar is low though - the cost of creating an account. They could always pay to have an account created and bypass this entire system.