The official stand is that we got the best PCIe riser for that price at that time
. 4.0 is achievable but as also dependent on which hardware you have, some configs have no issues running at 4.0 while others will have stability issues. There were other risers out there that were much more expensive (4-5x the price) and would have less* stability issues across more configs, but likewise would have cost you guys 4-5x more.
explained compatibility in more details a few pages back.
Now if the risers that are available from ADT today
existed at the time of pre-orders, we would have sold those instead as they are stable across more platforms. The cost would have been roughly 2x of what the pre-orders were at that time. Again, these new 50 USD risers are still probably not as good as the risers for 100 USD, but that is to be expected.
Tech is improving and new hardware is coming out, which is likely to create stability issues when paired with older riser tech. What I'm saying is that it's possible that PCIe 5.0 risers that are sold today may run into similar stability issues as new PCIe 5.0 hardware comes out.