>through some form of incentivisation (i.e no processing fees, like there are with CC and Debit cards)
The user pays processing fees upfront with their cryptocurrency?
Because someone still has to pay the fees for blockchain transactions, and the infrastructure pieces this scheme will need.
Your not using the blockchain anymore when you buy something with 'Credits', just as you aren't using the blockchain when you;
convert crypto to fiat -> use fiat in a shop.
That also has its own unique problems - if a retailer goes into bankruptcy, the gift cards are likely to be worthless (they're considered "unsecured debt"). Buying gift cards from a brand-new startup would be taking considerable risk.
Then there's the IT integration hassles, since existing closed-loop cards are coded into their POS etc. Adding "Credits" is going to take additional development - why are retailers going to spend money to do that?
The other option would be an open-network style card, but those are typically issued (again, in the US) by companies like MasterCard and Visa & carry the usual processing fees.
These fees are going to have to be higher than normal conversion fees, if you want to fund the credits operation - someone is going to have to pay for -
Alterations to the PoS software to accept credits Server infrastructure which can authorise the transactions Helpdesk staff to help out the shop staff when they get confused/stuck/whatever
Why would they do this?