[staticautomatic]

As a lawyer I think this could potentially be litigated as a breach of the implied warranty of merchantability.

[mrcsharp]

Would the question still be about measuring the drop in quality to prove that the product (the software in this case) is in breach of the law?

[staticautomatic]

Well, it would probably need to be part of a physical product and not software alone unless the vendor is dumb and forgot to disclaim the warranty (see https://repository.law.uic.edu/jitpl/vol16/iss2/6/).

Second, it’s not exactly about whether the change constitutes a drop in quality but whether it renders the product unfit for its ordinary purpose. The argument would essentially be that the change is a deliberately introduced defect.

It’s a little weird but a plausible claim given the right facts.