Checking the README for similarity to other packages can cause false positives for benign, legitimate forks.

Sure, I'm not saying those projects should be automatically deleted or something. Just that it's worth looking into. Maybe you put a message on the package's page notifying potential users and put it into a moderation queue. Maybe a volunteer takes a look at it, and if they find something, they hit the "report malware" button. Maybe you ask for confirmation if they try to add such a package on the command line.

Just spit balling.