I think that decision is much narrower than "market impact". It's specifically about substitution, and to that end, I don't see a good argument that Co-Pilot substitutes for any of the works it was trained on. No one is buying a license to co-pilot to replace buying a license to Photoshop, or GIMP, or Linux, or Tux Racer. Nor is Github selling co-pilot for that use.
To the extent that a user of co-pilot could induce it to produce enough of a copyrighted work to both infringe on the content (remember that algorithms are not protected by copyright) and substitute for the original by licensing in lieu of, I would expect the courts to examine that in the ways it currently views a xerox machine being used to create copies of a book. While the machine might have enabled the infringement, it is the person using the machine to produce and then distribute copies that is doing the infringing not the xerox machine itself nor Xerox the company.
Specifically in the opinion the court says:
>If an original work and a secondary use share
>the same or highly similar purposes, and the secondary use
>is of a commercial nature, the first factor is likely to
>weigh against fair use, absent some other justification for
>copying.
I find it difficult to come up with a good case that any given work used to train co-pilot and co-pilot itself share "the same or highly similar purposes". Even in the case of say someone having a code generator that was used in training of co-pilot, I think the courts would also be looking at the degree to which co-pilot is dependent on that program. I don't know off hand if there are any court cases challenging the use of copyright works in a large collage of work (like say a portrait of a person made from Time Magazine covers of portraits), but again my expectation here is that the court would find that while the entire work (that is the magazine cover) was used and reproduced, that reproduction is a tiny fraction of the secondary work and not substantial to its purpose.
Similarly we have this line:
>Whether the purpose and character of a use weighs in favor
>of fair use is, instead, an objective inquiry into what use
>was made, i.e., what the user does with the original work.
Which I think supports my comparison to the xerox machine. If the plaintiffs against Co-Pilot could have shown that a substantial majority of users and uses of Co-Pilot was producing infringing works or producing works that substitute for the training material, they might prevail in an argument that co-pilot is infringing regardless if the intent of github. But I suspect even that hurdle would be pretty hard to clear.