Motivation
People who buy coupon at low ESD price should get a longer expiration time.
Reason
We want more people to buy coupon when the ESD price is low but low ESD price means it takes longer time to get back to $1. This incurs more risk to people who contribute to the ESD price stability when the system needs it the most—this is not right and we actually want the opposite.
Note: all the price in this proposal refers to the TWAP price.
Solution
Link the coupon expiration time with the current price of ESD. E.g. $0.9 can be used as a baseline for standard expiration time (90 epochs).
Specifically, the coupon expiration time (t) can be calculated like so:
When ESD_price >= 0.9, t = 90 epochs;
When ESD_price < 0.9, t = int((0.9-ESD_price)*150) + 90 epochs.
Example,
ESD = $0.95, t = 90 epochs;
ESD = $0.8, t = 105 epochs;
ESD = $0.53, t = 145 epochs
As such, people who buy the coupon at low ESD price will enjoy a longer expiration time. This means less risk is incurred to them and they will be more willing to buy coupons when the ESD price goes down. IMHO, this proposal will help to stabilize the ESD price.
Difference from EIP-14:
EIP-14 is tackling the coupon expiration time problem from a different angle—more focus is on the risk/profit of a user. I doubt it will increase the sale of coupons when the system need it the most (when ESD is low).
This proposal links the price of ESD to the sale of coupons, giving people who buy at a low ESD price more assurance. This prevents the price of ESD from staying under $1 for too long and works especially well against the death spiral.
Plus, I also think a pure algorithmic method to deal with the coupon expiration issue is a nicer approach—auction based method add in more variables from human behavior thus less predictable.