Custody of the two assets has bordering on nothing in common.
Exchange of the who assets has bordering on nothing in common.
Conflating them is wildly innacurate.
I can figure some complex ways but somewhere, because there are not enough people using crypto, it will get exchanged and there you will be caught. In this scenario you are actually doing something illegal; spending money you did not declare to the gov for KYC/AML, so you can still be traced via the baker who exchanged your payment to euros. And if you used Monero or whatever, you are now an actual criminal trying to hide their tracks.
There would need to be a very large crowd accepting crypto for the crypto sake, not for the USD value to get anywhere here. Which is the dream of all the fans but this is not even close where crypto is currently and most govs are taking steps to prevent it getting there.
Currently, buying gift cards using the lightning network is faster than buying gift cards directly from merchants and there is no way Amazon or any other merchant can win the speed race using the traditional financial network.
From my understanding p2p exchange is the whole purpose of gift cards, so this activity is indistinguishable from other mainstream uses.