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.
Eh, kind of. Right now I'm hiring for a role where nobody remaining in my applicant pool is qualified (all have only some of the experience I need) but I'm probably still going to hire one of them. Does that "qualify" them? No. It just means I'm probably going to hire despite it.
I sell you a cat for $1B and you sell me a dog for $1B and now we’re both billionaires! Whether the capital markets “want” that or not it’s still silly.
Both parties would need the $1B prior to the transaction for it to even potentially be meaningful, and still they just traded a cat for a dog and only paid each other on paper.
That ultimately wouldn't be a big deal if the paper valuation from the trade didn't matter. As it stands, though, both parties could log it as both revenue and expenses, and being public companies their valuation, and debt they can borrow against it, is based in part on revenue numbers. If the number was meaningless who cares, but the numbers aren't meaningless and at such a scale they can impact the entire economy.