We have transactions fees, to avoid creating tons of transactions and increase the blockchain size to a extreme amount.
Those transactions fees are sent to the next user who is the miner.
How would the economy of a coin would change if instead of sending the transaction fee to be mined, the transaction fee was frozen and 1 year after it it would be sent back to the wallet. The user wont lose that money, but still can't keep making tons and tons of transactions to spam the blockchain.
It sounds like an appealing idea, but I feel that miners will be not rewarded enough this way, so they'll have a smaller incentive of confirming transactions. Also, would people really care about this kind of cashback? There were only a few times when I spend too much money on the fees, and most of the time I'm okay with the fees, so I would not care if my fees were returned to me now. I mean, it would be a nice little bonus, but not a game changer. So it's just not worth it to figure out how to implement it and not get miners angry over something that doesn't matter that much.