I'd assume the non-pros will remain on USB2, and that serves as a segmentation feature. Especially since only the pros can shoot in ProRAW and ProRES.
On iPads, the "base" iPad is on USB2 speeds, the mini supports 5Gbps, the air 10, and only the pro supports 40Gb USB4. And while SoC differences could explain differences between the iPad (A14) and Mini (A15), the 5th gen Air uses the same SoC as the 5th gen Pro which already did support 40Gb USB4. So it's not an SoC limitation.
Although they ended up putting the 48MP main camera on the non-pro and I thought that'd remain pro-exclusive as well so...
It's a bit more complicated than that with the iPads. The Mini supports 5Gbps but only as USB Host mode. If you hook it up to a computer as a USB client, it'll still be USB 2.0 [0]
If you're familiar with the Raspberry Pi 4, those do the same thing. That SoC supports USB 2.0 client. The USB 3.0 host is done through an external (to the SoC) USB controller, a VIA Labs VL805. That's what the Mini and iPad Pros have done. The first iPad Pro didn't even have a USB 3.0 to USB-A cable for USB client because it didn't support it, just their host mode accessory. The newer Pros probably do the 40Gb USB4 through a similar USB controller and only in host most. Not client, where it's limited to 10Gb [1].
I have an iPad Pro 11-inch 4th gen and that supports Thunderbolt/USB 4 but when connected as to my MacBook Pro it shows up as USB 3.1 at 10 Gbps. So that is correct.
It would definitely be a disappointment if they have the hardware on the device for 3, but arbitrarily limit to 2 for pure market segmentation. The iPad situation as you described it is discouraging.
On iPads, the "base" iPad is on USB2 speeds, the mini supports 5Gbps, the air 10, and only the pro supports 40Gb USB4. And while SoC differences could explain differences between the iPad (A14) and Mini (A15), the 5th gen Air uses the same SoC as the 5th gen Pro which already did support 40Gb USB4. So it's not an SoC limitation.
Although they ended up putting the 48MP main camera on the non-pro and I thought that'd remain pro-exclusive as well so...