Reviving this due to the inminent release of Zen 2...
As we know, whereas the Zeppelin die was a full blown SoC, AM4 Zen 2 (Matisse) has instead one or two CPU chiplets and an IO chiplet. However, from the perspective of the Processor as a whole unit, it is still a SoC. Moreover, for backwards compatibility, AMD had to make sure than whatever was exposed by Zeppelin is also exposed by the IO chiplet in a pin compatible format, so that the PCIe Lanes, SATA and USB Ports keep working if you drop Ryzen 3000 in existing AM4 Motherboards.
According to some info, Matisse IO chiplet and the X570 Chipset (And perhaps other derivatives) are based on the exact same design but manufactured in different nodes, the Matisse IO die is 12nm whereas X570 is 14nm. The Rome IO chiplet is an entirely different design and chances are that it is going to be used for ThreadRipper in a castrated format, unless AMD pulls out a third IO chiplet design, which I doubt given how similar ThreadRipper and EPYC 7000 are, and low ThreadRipper volume.
One of the problems with theorycrafting is that we don't know the full capabilities of the Matisse IO chiplet. For one, it seems that it has two widely different configurations, one in the AM4 package, which is limited in the exact same way that Zeppelin was due to Socket AM4 (24 PCIe Lanes, 4 USB), whereas in Chipset variant, there are things like the 128/144 Bits (Or 2 x 64/72?) Memory Controller and the Infinity Fabric links to connect to the CPU chiplets that are not exposed (Unless they're multiplexed into something else). The miscellaneous I/O seems to not be exposed, either, given the fact that it is already available on the AM4 Socket. The status regarding the 10G MACs is unknow, but given than it wasn't very popular in Ryzen Embedded and EPYC Embedded, it may be possible that it was removed, but we have to wait for a product to use them to know if they are still there.
What info we have available about the Matisse IO chiplet capabilities comes from AMD own slides:
https://newsbeezer.com/czechrepubliceng/amd-x570-chipset-and-computex-motherboard/
Pay attention to slides "AMD X570: THE MOST MODERN I/O" and "AMD X570 CHIPSET: FLEXIBILE LANES AND CONFIGS".
X570 has 4 PCIe Lanes for the Processor uplink, 8 dedicated PCIe Lanes and two pairs of 4 PCIe Lanes that can be configured as PCIe or SATA, for a total of 20 PCIe Lanes or 12 and 8 SATA Ports. On top of that, there are also 4 dedicated SATA Ports, 4 USB 2.0, and 8 USB 3.1 10 GBits p/s. This is a quite different arrangement from how it is used in AM4, since we are missing 4 PCIe Lanes, however, we don't know the full list of multiplexed stuff.
Compared to Zeppelin, the Matisse IO chiplet seems to have less PCIe Lanes (Bare minimum 24 to match Socket AM4, we don't know if it has 32 like Zeppelin). However, the extremely interesing stuff is the increased amount of USB Ports. Now you have a total of 12 compared to only 4 in Zeppelin. As I stated before, when using Zeppelin as a SoC, the scarse amount of USB Ports made it hard to use it to drive a consumer computer without a third party USB Controller (Supermicro abused onboard USB Hubs in their EPYC Embedded Motherboards), whereas Matisse IO chiplet can confortably fill that role without help, making it better than Zeppelin. Basically, Zen 2 as a proper SoC suddently makes even more sense...
As things are, we don't know when a Zen 2 based EPYC Embedded would appear, nor what its chiplet composition or full set of exposed features is going to be. Assuming that the Matisse IO die has 32 PCIe Lanes, it could be pin compatible with the first generation of single Zeppelin EPYC Embedded models, at the cost of the new USB Ports. However, there are
EPYC Embedded based on two Zeppelin dies, being functionally equivalent to a 16C ThreadRipper with 64 PCIe Lanes and 2 x 128/144 Bits Memory Controllers. As the Matisse IO chiplet should have been designed with AM4 in mind (Unless AMD likes to waste silicon), a possible 16C Zen 2 EPYC Embedded would actually be identical to the AM4 counterpart (Same IO chiplet, 2 CPU chiplets). Given the fact that the double die EPYC Embedded are nowhere to be found (At least I don't remember ever seeing a Motherboard with them), and that to make a Zen 2 successor AMD should use either a giant Rome IO chiplet or a new ThreadRipper IO chiplet design, chances are that AMD will not directly supercede the double die EPYC Embeddeds with a Zen 2 ThreadRipper level replacement. I don't even think that it can fit in the current PCB size, so it means a new, bigger embedded format not compatible with what they currently use.
Matisse in an embedded format not only seems even better than Zeppelin, it even makes MORE economic sense, given the stupid premium that X570 Motherboards seems to carry. I'm even more confident that we have to get rid of the Chipset in mATX form factors and below.
On a sidenote, I recently saw an EPYC Embedded Motherboard, the
AsRock Rack EPYC3251D4I-2T, which is interesing because it has an OCulink Port that can be configured in either PCIe (For NVMe) or 4xSATA mode. SATA Drives are connected via breakout cables like
this one. With Matisse IO die two pairs of configurable 4 PCIe Lanes or 4 SATA Ports, you can have two OCulink Ports in a Motherboard and drive either two NVMe Drivers or 8 SATA. While native OCulink NVMe SSDs are not common (If they even exist), you may manage to use them for M.2/U.2 with adapters (However, that adds to the cost. Cables are expensive, too). Regardless, I think that using OCulink with the breakout cable is a superior option to having 4 standard SATA Ports given the fact that you can't use them for PCIe, whereas with an OCulink Port you still have such option.