I don't normally get into the speculation station but I am working on piecing together my AM4 build and have been thinking about picking up an x470 board and a 2600X now while I let the dust settle with everything else. The only hold up I have is what will x570 bring to the table that x470 doesn't have. I thought pcie4 would be the primary feature but it appears that pcei4 will be available all the way back to x300 boards and will be up to manufacturers to implement. I would expect most highend x470 boards (Asrock Taichi Ultimate, etc) will get that feature. The only other feature I would expect is enhanced power delivery for the bigger chips but I would imagine the higher end boards will cope just fine.
So, what is left?
So the story about backwards support for PCIe 4.0 is this. Some motherboards may support it, but it comes down to how well the motherboard makers made the signal layers between the first x16 slot and the CPU, as only this slot would get PCIe 4.0 support. On top of this, the board makers would have to qualify the boards for PCIe 4.0, which they might not do. Lastly, a new UEFI would be needed to make it all work, which the board makers may or may not do. I would expect to see at least a few high-end X470 boards get PCIe 4.0 support, but it won't be all boards, that's for sure. The X370 boards are not likely to get it.
X570 will be quite different from the X470, it's afaik not made by ASMedia. There will be support for more NVMe drives, more USB 3.1, but less SATA. It will also be more expensive, as the boards are going to need re-drivers/signal conditioners to work properly with PCIe 4.0 and these are apparently not cheap. Not all X570 boards will get full PCIe 4.0 support as well, due to this additional cost, so make sure you know what you're buying once it becomes available.
Personally I would wait for the new gear, as my understanding is that it will be significantly improved all around.
Ryzen 3000 is still 5~ months out.
Pcie 4.0 might be useful for allowing x570 boards to support more than one Native pcie full speed nvme slot. This is something I wanted on x470. For example you may have dual pcie gen 4 M2, with 2 lanes each. These would provide same BW as current gen3 4* slots.
I don't know where you get your info, but that's plain wrong.
Without bifurcation or some kind of PCIe 4.0 to 3.0 bridge chip, that wouldn't be possible, unless you're talking about boards with 2x PCIe 4.0 two lane slots, instead of four lanes slots. This is unlikely, as current PCIe 3.0 SSDs would run at half speed then. There are also exactly zero commercial availability of PCIe 4.0 SSDs and there have only been one or two new controller demos so far, so don't expect any PCIe 4.0 SSDs until late this year or early 2020. Those drives will be high-end drives as well, not two lane drives.
