Personally, I'd like to figure out how to use a SATA controller as a high speed serial port. Swapping pairs on a 6 Ghz cable will be dicey, especially compared to the old RS-232 cables and DB9/25 connectors, but it should be possible to have comms between PCs via spare SATA ports.
I think that plan would run into problems with too much functionality being hard-wired in SATA controllers. There are plenty of off-the-shelf solutions for PCI Express, though.
