would the SSD need to be designed to use pcie 4.0? then old devices would be inefficient lane hogs?

yes, correct

thanks. im still gonna be using some PCIE 3 stuff for a while so i guess im still looking at TR4/threadripper. will continue to watch and wait and watch and wait

i don't think the current consumer hardware ecosystem really makes that possible before 2020 at reasonable price points, but pci-e 4.0 is already making inroads on workstation and hpc hardware

most things the average consumer would use are not bandwidth or installation density limited

Is there a roadmap on planned future development?