not to beat a dead horse, but in my opinion, the move to pcie from sata for hdd and other devices seems to be what will drive the need for the bandwidth. if the latest and greatest cards barely use what is available, it will take a very long time for new cards to need it. by then pcie 5.0 will be out with 4x the bandwidth now and we will still be having this conversation.
but moving many other devices to the pcie lanes will create the demand for more lanes and more bandwidth on them.