That sounds like a viable workaround to some of the problems with strictly-regulated economies. It would be great to see something like that spring up in Argentina.
how should the merchant physically accept the bitcoin purchase when the he doesn't have any smart devices?
Either the merchant or the customer has to have a device allowing some sort of internet access; even trading Casascius coins or bitcoins stored in private keys printed to paper requires checking the address to make sure it is actually funded.
If the merchant is relying on the customer to have a device to send the transaction, then one way to accept the transactions is to pre-print the payment addresses. The merchant can generate a few thousand payment addresses onto paper (or ask his service provider to do so.) Each paper could have a QR-code of the payment address, the full text of the address (in case the customer has to actually type it in) and an empty space for jotting notes. The merchant shows the QR-code to the customer, watches him send the bitcoins, then jots down any important info (amount, item sold, etc.) in the blank area. If the number of customers spending bitcoins is small enough that it won't create difficulty with the accounting, the merchant could instead have a permanent payment address on a nice display next to the register, and ask the customers to make their payments to that address.
Granted, it would be far better if the merchant could at least check the blockchain to verify that the transaction has been sent; but if that's simply not possible, then at least this would allow honest customers to make purchases, even if it allows for thieves to merely pretend they sent the coins.