I don't think so. Pre-x470 boards aren't supposed to support PCIe 4.0, so there's no need to offer support for such a functionality. Every mobo model needs its own bios release anyway, so a manufacturer could check some of their models to see if the first 16x port seems to work with PCIe 4.0. If it seems to, make the bios switch visible. Add a warning to it, perhaps. However, like I said, I don't see why they would do such a thing from a practical point of view since it could rob them of some new sales. I might even believe they have had some talks about this with AMD, to see what sort of incentives each generation would offer, to balance the CPU compatibility remaining there, as opposed to Intel's scheme. So far the generations have had at least something little. PCIe 4.0 might be the main thing for x570. It would certainly be more visible in marketing than x470's benefit over x370.