[yangff]

Sounds like clean room, and if you can do that for GPL code, you can also do that for proprietary code, which is fair in a sense. Or maybe the question is whether you can re-label the code so written as GPL or MIT ......Or, you should let GPT pick a license that it likes.

[thomasahle]

You can also decompile a proprietary binary, ask GPT to rewrite it, and then re-release it as your own work.

Somehow I feel the lawyers won't agree.

[visarga]

Reimplementing would also help with training data, it's a way of extracting the idea without copying the original form. Works even better on images with variations, you generate the style from image A with content composition from image B, thus extracting the style without the exact expression.