Sorry, but this is NOT marketing BS and it NOT about selling more boards.
I dont agree with that - it came out as an AGESA beta and the mobo manufs publicly released it, fast.
With the amount of variation between all the revisions of these boards, what would have happened if certain boards just black screened on POST with a 3090 or 6x00 card once PCI-E 4 was mainstream?
I preemptively apologize for off-topic, but PCIe 4.0 is near-identical to 3.1 from electrical perspective.
The only differences are:
1) Tighter tolerances for signal loss (mostly handled on RX/TX side)
2) Higher susceptibility to crosstalk (needs minor adjustments to ground pins and via placements)
On short distances neither is going to cause major issues (assuming board partners didn't skimp on parts and followed PCIe 3.1 spec). Worst case - it'll fall back to gen3.
Think of it as running 10GbE over Cat5e in an apartment or overclocking your RAM. It's not "compliant", but works just the same.
There are many exceptions (boards with older redrivers or PCIe MUXes etc), but the principle still stands.
Nothing drastic to cause mass-outrage towards AMD, or bash Gigabyte and Asus for deploying a new feature. And no one said "all boards". AMD only mentioned 400-series boards, and board partners narrowed it down to only certain models, and later added a couple X370 (like OPs Crosshair 6, or GB X370 K7). ASUS even went as far as doing proper compliance testing, hence only a dozen or so motherboards got on their list. Main reason: x570 too expensive, B550 delayed again, and neither AMD or board partners weren't sure if AsMedia will ever go through with it (remember, the miracle update came out in early 2019, while B550 didn't come to fruition 'till summer of 2020).
Call me a conspiracy theorist, but please tell me that my rambling makes less sense than $80 B550 board which has even worse layout than its predecessor and has decoupling caps nearly twice as far away as older boards, and no recommended adjustments for crosstalk reduction, is more fit to drive PCIe 3.0 bandwidth than last-gen flagship solution. Heck, some "lucky" B550 owners have already encountered PCIe 4.0 issues on their boards (long POST, fallback to 3.0), and that's supposedly a fully-compliant design....
The OP has an X370 board and I hope you're not seriously implying that AMD should've made the board makers design in PCIe 4.0 support back when that board was launched?
It's not about designing the board with PCIe4.0, it's about the existing design being capable of 16GT/s.
OPs board with 7201 update in action: