We'll see if they even make them. I can't imagine there's a huge customer base who really needs to cram all that I/o through only two or 4 lanes. Why make these ubiquitous cards more expensive if most of the customers buying them are not short PCI-E lanes? So far most making use of 5.0 are graphics and storage devices. I've not seen any hint of someone making a sas or 10 gbe card that uses 5.0 and fewer lanes. Most cards for sale today still use 3.0 let alone 4.0.
I might as well just drop the cash on a real EPYC CPU with 128 lanes if I'm only going to be able to buy cutting edge expansion cards that companies may or may not be motivated to make.