It doesn't seem like it is possible to create a coupon that offers the user a free shipping method or eliminates the shipping fee altogether.
I have been able to create a free shipping method using the shipping module + flat rate + rules for orders over X amount, but I would prefer it if the user has to enter a coupon code in checkout. This way the admin can turn the coupon on and off as they see fit (seasonal promotions) and they can give out a limited amount of codes for their users (If they did not want everyone to have the promotion).
A good way I see this being done is if a coupon can be a 'condition' rule for flat rate shipping. I.E. have the free shipping rate check to see if the coupon code is entered and then offer the rate to the customer when they select shipping method. Though I am not sure if that is possible. Thanks for a great module!