The quote “On a WHCP-certified USB 40Gbps system, you can also plug in any USB4 or Thunderbolt 3 device and trust it will work every time on every port” makes it sound like if you include one USB4 40Gbps port, then every Type-C port must be a Thunderbolt-compatible USB4 40Gbps port that supports every TB3 feature. That certainly does change the equation, because 2x USB4 + 2x USB 3.2 (with DisplayPort and charging) is not a configuration that will pass certification. You’d have to make all four ports USB4/TB3, drop all four ports down to USB 3.2, or stick with two USB4 and omit the other Type-C ports for that consistency to be true. Microsoft wants everyone to do the first one at no extra cost, but it doesn’t seem likely to me that laptop OEMs are all going to shrug and absorb the cost just because it would be convenient for Microsoft if they did.>I feel like the maliciously-compliant OEM approach to this would be to just provide less type-C ports, and/or choose to leave USB4 out of machines that would otherwise get one "better" port
The number & type (speed) of USB-C port is a marketing upsell, ie higher-tier products get more/faster ports. The MS mandate doesn't change this equation.
The new MS standard doesn't change that much. USB4 is based on TB3 and compatibility is already required, just not every TB3 feature is supported on some (cheaper) implementations, eg PCIe tunneling. Now it will be.
The only major changes are video-out (DP Alt) will work on USB3, and full TB3 compat on USB4. The mandate doesn't change charging & data speed; it just standardizes them.
Sleep/wake functionality is IMO a bigger deal than most realize. Good to see it's included in the mandate.
Lastly, OEMs don't need to comply with the MS mandate. Those w/o compliance just won't get WHCP cert, and can't be marketed as "Certified for Windows." It doesn't mean Windows can't run on those devices. I imagine all mainstream OEMs will comply, but lower-tier white-label boxes may forgo the cert.
Given that I’ve never seen “Certified for Windows” pushed as a marketing point for home users, I’m guessing there’s some other stuff attached to that beyond being allowed to put that phrase on the box, and OEMs like Dell and HP will be pressed into compliance.