Recurring/Lifetime Coupons for Pro Sites

This is a feature request.

Currently, Pro Sites Coupons are only applied one-time at purchase.

Requesting an option to make coupons recurring. I.e. allow an option for the discount to be applied on a recurring basis (for 3, 6, 12 months) or indefinitely (lifetime discount).

The existing setup screen is great (it's simple), but the addition of the ability to change duration would be perfect.