Asus has posted a statement detailing which of its motherboards will be compatible with the upcoming next-generation Ryzen 3000 series of processors from AMD. The list covers models from the 300 and 400 series of products, and Asus has added that further motherboards will be included on the list soon.
https://www.notebookcheck.net/Asus-reveals-full-list-of-AM4-motherboards-that-will-get-BIOS-updates-for-AMD-s-upcoming-Ryzen-3000-CPUs.419816.0.html
will asus x470 get pcie 4.0 update?
No. X470s don't have the circuitry required for PCIe 4.0.