That's a decent idea. I see that you guys already send out e-mails and then I feel like I was left out when my product isn't on it.
The only thing that concerns me about your idea is that the e-mail would get over populated with content.
Perhaps the system could be smart. For example... (Not saying it's a good example) If you send an e-mail out each week you could look at which category that customer purchased from... I.E. customer purchased an Audio product. Then you send only those coupons which are in the category they last purchased from. Therefore that customer would not see coupons from products in the E-Textile category.
I'm sure there are other ways it could be smart and limit the number of coupons the customer is bombarded with at one time.
I can foresee sellers abusing the system and perhaps making their prices a little higher and offering coupons each week just to be on the e-mail.
One other way may be to limit entries to the e-mails to 12 per year. You can do up to one a month or if you think one month is slower you can do 4 in a month and skip 4 other months.