It would make sense for Amazon to raise the price rather than disallowing it (specifically, because enforcing a prohibition on activity would cost Amazon money, but setting the price to be at least marginally more expensive than Amazon's expected minimal-effort realizable gain from using the GPU instances themselves would make Amazon money.)
It would make sense for Amazon to raise the price rather than disallowing it (specifically, because enforcing a prohibition on activity would cost Amazon money, but setting the price to be at least marginally more expensive than Amazon's expected minimal-effort realizable gain from using the GPU instances themselves would make Amazon money.)