I don't think IPs were ever a viable tracking tool besides detecting the country. NAT has been the default for most home networks and as a marketer you really don't want to confuse a mid-forties dad with their 14 year old daughter. So you've always had very very different marketing profiles share an IP. Besides that browser profiles are just soo much more exact.
>I don't think IPs were ever a viable tracking tool besides detecting the country.
That depends on the ISP.
Many cable ISPs assign DHCP blocks to nodes that are defined by geographical areas. These can then be correlated with cellphone apps on wireless connections that also return GPS data to the collector. After a few thousand samples you get a really good picture of IP blocks that move and ones that are somewhat static.
