Based on my own experience as a peer reviewer and scientist, the issue is not necessarily in detecting plagiarism or fraud. It is in getting editors to care after a paper is already published.
During peer review, this could be great. It could stop a fraudulent paper before it causes any damage. But in my experience, I have never gotten a journal editor to retract an already-published paper that had obvious plagiarism in it (very obvious plagiarism in one case!). They have no incentive to do extra work after the fact with no obvious benefit to themselves. They choose to ignore it instead. I wish it wasn't true, but that has been my experience.
During peer review, this could be great. It could stop a fraudulent paper before it causes any damage. But in my experience, I have never gotten a journal editor to retract an already-published paper that had obvious plagiarism in it (very obvious plagiarism in one case!). They have no incentive to do extra work after the fact with no obvious benefit to themselves. They choose to ignore it instead. I wish it wasn't true, but that has been my experience.