Well, this is an interesting idea, but it has one small drawback.

I’d assume that legitimate sites would not block the Wayback Machine completely. Even a pay-walled site would have a login page. I’d expect a site with a full timeline to be more likely to be legitimate than one with only a few recent crawls.

This wouldn’t catch long term fake sites, but would be an indicator for ones that are spun up for a single campaign.