Interesting concept. I don’t know anyone who has this pay scale system in place so I can’t give you any insight as how it works for them. The only issue I see with this system is that makes things complicated. You will need to consult with your accountant and make sure this won’t be an extra headache for you as far as taxes goes. Also, this system seems to be a great alternative for those who cannot afford to pay the full asking rate and you are the one who must do the potential client’s income (for me this is too confusing and time consuming, but you might have already figure it out).
At the end of the day it comes down as to how much money you want to earn or you think your time worth. I’m not sure my answer helped you at all, but I guess it’s better than nothing. Good luck to you and I hope to see others put their suggestions here.