News out of Hong Kong have introduced the B550 for the entry level systems. The B550 uses PCIe 3.0 however with a Ryzen 3000 series processor the SSD and graphis cards will be provisioned with PIe 4.0 speeds. The slower speed is only to the PCH.
The B550 has fewer SATA channels which mean most board will offers 4 headers while X570 have 6 SATA channels. The B550 also has fewer USB 3.2 but it does offer 6 USB 2.0 ports. The front panel USB ports are mostly used with USB sticks. Board makers may offers type C support given the growing adoption of the new standard.
AMD enthusiasts can expect to see machines with B550 motherboards late in 2019 and bare motherboard should be available in 2020.