ASRock has started putting stickers on the packaging of its H310 motherboards indicating that the upcoming 8 core Intel CPUs such as the Core i9-9900K and the Core i7-9700K are supported by the H310 chipset as well along with the Z390. Existing H310 boards should be getting a BIOS update that enables support for the new CPUs.
https://www.notebookcheck.net/The-Intel-Core-i9-9900K-and-the-Core-i7-9700K-will-be-compatible-with-H310-boards-as-well.318606.0.html