Limiting any user to where they can spend money would be...

Limiting any user to where they can spend money would be suicide.
Limiting their ability to pay off their debt via one source would also be suicide.

Zip has plans to add a feature to be like 'honey' (but I guess they said they had plans for Crypto, which hasn't eventuated too).

A tiered system could be good, but you shouldn't charge for it. It should be based on amount spent in a certain timeframe. Like the casino - play for certain amount of hours and put through a certain amount of money to get free parking, discounts, exclusive events etc etc.. Zip makes money for every transaction.. so get the customer to spend more to achieve the next tier. More points earned if shopping at partnered merchants, bonus points to buy certain items said merchants want to sell more of etc.