First of all - thanks for detailed write-up and pictures. This was info I've been looking for last several days.
And to some others, IMHO, you're stressing too much.
If I'm not mistaken this could be possible as B650 "E" ITX board:
HDMI+DP
1x x16 PCIe 5.0 (for GPU)
1x M.2 via x4 PCIe 5.0 (from CPU)
1x USB 2.0 (from CPU)
3x USB 3.2 Gen 2 with DP mode (from CPU)
1x USB 3.2 Gen 2 (from CPU)
2x USB 4 (from CPU via x4 PCIe 5.0)
2x SATA (from B650)
1x M.2 via x4 PCIe 4.0 (from B650)
1x 2.5 GbE (via PCIe 3.0 from B650)
1x WiFi (via PCIe 3.0 from B650)
6x USB 2.0 (from B650)
4x USB 3.2 Gen 2 (from B650)
1x USB 3.2 2x2 type C (from B650)
Does that sound like low end ITX board? That's what CPU with single chipset can give you. And all can be used at once (as in, nothing will be blocked if you plug in something else). Full PCIe x16 5.0, two M.2 drives, 2 SATA drives, 18 USB ports, Ethernet, WiFi, and up to 4 displays. (That's just example, I'm sure there will also be something like "home server" ITX boards with 2 network ports and 8 SATA ports instead USB 4 and WiFi such)
Now to expand on that, a full ATX X670E board (2 chipsets) can do something like:
HDMI+DP
1x x16 PCIe 5.0 (for GPU, or 2x x8)
1x M.2 via x4 PCIe 5.0 (from CPU)
1x USB 2.0 (from CPU)
3x USB 3.2 Gen 2 with DP mode (from CPU)
1x USB 3.2 Gen 2 (from CPU)
2x USB 4 (from CPU via x4 PCIe 5.0)
6x SATA (from chipsets)
2x M.2 via x4 PCIe 4.0 (from chipsets)
1x 2.5 GbE (via PCIe 3.0 from chipsets)
1x WiFi (or x1 PCIe 3.0, from chipsets)
1x x4 PCIe 4.0 (from chipsets)
12x USB 2.0 (from chipsets)
8x USB 3.2 Gen 2 (from chipsets)
2x USB 3.2 2x2 type C (from chipsets)
That's again a crazy total, like full PCIe 5.0 x16 slot (or two x8), x4 PCIe slot (or a few x1 slots), three M.2 slots (!), Ethernet+WiFi (or dual LAN), 6 SATA and up to 29 (?!) USB ports, and again no small print like "using M.2 disables 4 SATA". (And again that's just example)
I could live with that ITX "B650E" board actually, I have been thinking past several days, and I can't remember when I used anything in PCIe slot except GPU (ages ago a satellite card), always juggled 5-6 SATA drives but I can do with 2 M.2 + 2 SATA with current capacities, my days of needing 2nd LAN are gone, and WiFi can be a backup interface, and everything else can just go to USB, specially with USB4. I honestly think I can move away from ATX and E-ATX boards with this generation, and move from tower to SFF PC.
IDK, to each their own, choosing MBO is always a personal choice for tech enthusiasts, but I see no negatives with this AMD setup. Those few people that will somehow see it as flawed can always go for something like HEDT / workstation PC, be it Threadripper or Xeon or whatever.
P.S. And I loved that "no chipset" idea, I'm sure OEMs would be all over it with SFF office PCs and the like. Are we sure it's not an option? Did anyone actually say so (from AMD or MBO makers)?
Edit: typos if there's more pls excuse me