GCP patched a similar loophole [1] in 2023 presumably because some of their customers were abusing it. I'd expect AWS to do the same if this becomes widespread enough.
Unlikely. The "loophole" GCP patched was that you can use GCS to transfer data between regions on the same continent for free. This is already non-free on AWS. What OP mentioned is that transferring data between availability zones *in the same region* also costs $0.02 per GB and can be worked around.
This doesn't feel like a loophole though, it feels like they have optimized S3 and intend your EC2 instances to use S3 as storage. But maybe not as transfer window, that is, they expect you to put and leave your data on there.