Wouldn't this very likely mean that a lot of your users hit a wall immediately, without being able to use any credits?
for example, i have 900 users, 7% paying, but it's 3-6 new users per day, it's manageable at 5 credits per user per day (non-renewable), and 20 communal (so in theory 4 users)
when i grow, i just raise the communal credits from 20 to, let's say 100, so 5x more free happy users per day. i think it's beautiful in its simplicity and flexibility