Everything you guys are talking about has already been done and is currently being done...
The big data sharing network to match IP/Cookie to email/phone/address? Yeah BlueKai and it's match partners and all it's competitors have been on that for years now. Using random sites people give email/address to they match you to your Experian credit profile.
The issue is always accuracy and match rate. Facebook came into the game in 2012 and has been blowing people out of the water on it.
Facebook and Google both have the data to expand this market quite a bit but they are smart enough to realize they don't want government regulation on this stuff so they've kept it at bay enough not to spook the average internet user.
