Thank you on your feedback regarding the CP091 concept product. If you seek to put this kind of product in a 5.25" drive bay, we have the MB343SP bracket that would allow usage of a 3.5" device in a 5.25" drive bay.
As for PCIe 4.0 compatibility, this concept product was created before widespread adoption of PCIe 4.0. However, it is very likely this concept product, if fully developed, will incorporate PCIe 4.0 support on transfer speeds.
If you have additional thoughts or comments on our concept products, feel free to make a message on the forum topics.