1) Maybe lead in the ground has the same general level of danger as lead paint? Other sources of lead were covered in the article.
2) It is possible (probable even) that the levels of lead have been retarding the growth of IQ, but not reversing it.
3) Ignoring that even your link mentions that the data is skewed due to higher survivability as medical technology has gotten better, this is a separate trend on a separate scale and not really all that relevant. It could possibly be explained by lead from other sources (plumbing maybe?) or other factors outside of the scope of this particular study. If anything, your link reinforces that there was an issue as the homicide rates climbed sharply before suddenly dropping off again.
Not unless they decide to completely revamp how addresses are assigned, no.
Edit: and to address the comment that slipped in just ahead of me...MAC addresses as a part of IPv6 addresses are fine. If the interface is on several subnets, then the network portion of the IP address will be different.
Edit2: To clarify my initial comment, as the other commenter stated, there is no effective way to handle the routing for keeping the network portion the same, so that would always depend upon where you are. The only possibility could be to be assigned a permanent host ID, but considering how many devices the average person has with network access (I have a couple dozen easily, but I'm not average,) I'd think that this would be impractical anyway.
A company asking for this potentially opens themselves up to a huge amount of legal liability since a typical Facebook profile can contain an enormous amount of data that they are not allowed to ask during the interview process.