Are there products on the market that uses these already?
I have been reading
this article and was really furious at how Zen was capped by Socket AM4, as it seems that they designed it with the previous Excavator/Bristol Ridge in mind instead of making full use of Zen. 24 PCIe Lanes instead of 32, lack of the up to 8 SATA, no 10 GBit NIC, and this coupled with the lack of Workstation oriented Motherboards as there is no official ECC support nor IPMI.
Then I just noticed that there is a good analogous to the Ryzen 7 1700 in the Epyc Embedded line: The EPYC Embedded 3251. It is a fully featured single Zen die with everything that was left out of AM4. For a mATX build, you could get rid of Promontory and drive everything from a Zen SoC. The only thing where Zen feels a bit limited is in just 4 integrated USB 3, which means that maybe a third party USB Controller may be required, but otherwise Zen is just perfect. Wouldn't mind losing upgradeability, through I doubt that overclocking is possible and you're missing around 1 GHz worth of performance compared to a Ryzen 7 1700/1700X/1800X. Still, if price is right looks like a true beast to me.