One way to implement a token-based discount is that whoever owns/holds a token gets the discount. Another way (that I had in mind) requires you to transfer it back to the store. In this case it is lot more convenient to transfer both BTC and Counterparty token in the same transaction.
It actually is implemented, both in the CLI and the API, at a per-transaction level:
Cool, I believe such transactions will be common in the future.
An example is Alice the Musician. She sells her mp3's for 0.05 BTC each. She realizes that she can reward fans who blog about her, write in forums, etc, by giving them a discount token, ALICECOIN. One Alicecoin is backed by a 0.01 BTC discount.
When buying with discount, the buyer transfers 0.04 BTC + 1 ALICECOIN in one transaction.
A huge advantage for Alice is that there are no direct costs with issuing the coin, but the fans who anyway would buy mp3's see a real value in it. Holders of the coin who do not want to buy her music - even with a discount - will try to sell it on the DEX. If she gives away a reasonable amount of coins the market price should be slightly less than 0.01 BTC.
I find the proposal very interesting and it definitely adds to the list of another use case for tokens.