Bundling a physical good with a digital one has been done before, so if I understand correctly the only problem here is that the usage of a t-shirt is purely to circumvent the ban from the bank (due to high chargeback rate)...

In that case, and theoretically, bundling the physical good with a digital access right from the start would be perfectly legal right?

It would still be a dodgy way to reduce chargebacks, but assuming no bank ban occurs, it shouldn't be a breach of contract.