Followed the Area 51 proposal for this site before it entered the commitment phase
None of these sites had Area 51 proposals.
In addition to Popular Demand's "funny because it is true" comment ..
[Precognitive badge] teaches an important lesson to people who try to earn every last badge.
The Precognitive badge appears in the badge list on every site to announce the presence of Area 51, and its primary function.
Since Area 51 is itself about creating new sites that don't exist yet, the thought process is supposed to be:
hmm, I can't get [the precognitive badge] on this site, but I could get it on some hypothetical future site I might be interested in.
Yes! Thus, based on seeing this badge and reading about it, a user is incentivized to:
In conclusion: win.
The only minor downside is that Precognitive could incentivize following a lot of proposals you don't actually care about in hopes of getting the badge by chance. But this is really no different than the "fill out my profile with a bunch of garbage" approach to getting the Autobiographer badge. So the risk is very small, it's just a bronze badge, and the upside is IMO large.