PCIe Gen5 is now available in the latest Intel desktop processors. There are very few lanes, so it can really only run a single GPU, but that's covers a lot of the potential market.
[1] https://ark.intel.com/content/www/us/en/ark/products/series/...
[2] https://ark.intel.com/content/www/us/en/ark/products/134598/...
[3] https://ark.intel.com/content/www/us/en/ark/products/132214/...