According to the Taiwanese publication, the integrated-circuit design company owned by Asus is "expected to land contract design orders for all mainstream PCIe chips from AMD even after the U.S. chipmaker rolls out X570 motherboard chipsets that support PCIe 4.0". Our own motherboard sources have told us that AMD could continue to incorporate ASMedia elements into parts of the chipset, such as USB 3.1 support.
ASMedia is a pretty well-known name in the motherboard field. The company is mostly responsible for providing third-party USB, PCIe and SATA controllers for both AMD and Intel motherboards. As a matter of fact, ASMedia was the one who designed and produced AMD's Promontory chipsets, such as the 300-series and 400-series for the chipmaker's Zen processor microarchitecture. So when word of AMD designing the X570 chipset in-house got out, many thought AMD would ditch ASMedia.
AMD processors have been exposed to a few vulnerabilities in the past through ASMedia's chipsets. Correcting the issues takes a while as AMD has to go through ASMedia to do so. Therefore, having a more direct control over the design process could be a reason for AMD to go with an in-house design.
However, there's just one inconsistency with Digitimes' report: the time frame. The article says ASMedia will not complete the tape-out for PCIe 4.0 until the end of the year. However, the penultimate paragraph claims ASMedia will roll out tape-outs for PCIe 4.0 by the end of of the year.
AMD is expected to launch its Ryzen 3000-series processors roughly around Q3. One of the new chips' selling point is support for the PCIe 4.0 interface, so naturally AMD will want X570 motherboards available to customers to house them, one way or another.