They will come! I saw a modem running on PCIE on a Cebit 2005 picture.
But I agree that most PCI card aren't migrate to PCIE yet because, well, there not a lot of PCI card left on the market. Network, Network are usually merge in motherboard now. Sound with AC97 or new Intel High Definition Audio. There is not more left on PCI but don't forget that even with no PCI card, the southbridge is limit to 33 MHZ. That mean max 133 MB for hard drive, USB 2.0 and everything else connect to the SouthBridge. With PCIE, the SouthBridge can finally be fast!