Currently, AMD's X570 chipset is produced in-house, a change from previous 400-series and 300-series chipsets being produced by a third party, and it seems as if X570's successor, the alleged ‘X670’ will return to third-party production.
AMD's 600-Series Chipsets to be Outsourced
According to a report originating from MyDrivers, AMD's upcoming 600-series chipsets will be outsourced similarly to how ASMedia produced AMD's 300-series and 400-series chipsets, and other rumors point to the B550 chipset being produced by ASMedia as well.
B550 continues to utilize an eight lane PCIe 3.0 downstream link for general purpose use and a four lane PCIe 3.0 chipset bus, though B550 may still be capable of PCIe 4.0 connectivity if paired with a 3rd Generation Ryzen CPU through PCIe 4.0 x16 and PCIe 4.0 M.2 slots.
X670 - Passive Cooling & Increased Efficiency
As far as the alleged successor to X570 goes, 'X670', may be built by a third party such as ASMedia or another entity. With X670, both the chipset bus and general purpose PCIe lanes will be PCIe 4.0. Currently, X570 chipsets are known to run significantly warmer than their predecessors, though it seems as if some extra heat is the price to pay for speedy PCIe 4.0 connectivity. X670 may change this, and it is possible that the primary goal of X670 is to reduce the amount of heat expelled from the chipset and return to cheaper, fanless chipset cooling solutions.
Chipsets or I/O Dies? AMD's Resource Allocation
In general, the chipset market is fairly low-margin, therefore, AMD would rather allocate chipsets as I/O dies found within Zen 2 CPUs and let another entity handle the chipset market.
GlobalFoundries manufactures the chips used as either I/O dies in Zen 2 CPUs as well as chipsets, and for AMD, using those chips as I/O dies is increasingly efficient in terms of revenue when compared to using the same chips for chipset implementations. For AMD, in the long run, outsourcing chipset production is in its best interest due to R&D allocation to more pressing matters, as well as cutting back on additional financial strain of another division dedicated to producing chipsets.