I'm also well aware of the cost and the difficulty of maintaining the code for the "evolving" kernel...
But, as other sayd, it's for an IOT project, rare update, not connected to internet/cloud, with very low security needs.
If on the critical and security fixes only phase of a long term release for a kernel package from an Enterprise focused Linux distribution then "evolving" is on a much slower track, so much of that maintenance effort is mitigated.
Also, you had mentioned ultrasound device. While all Linux kernel internal interfaces are subject to change, a device like that is not subject to the bleeding edge in making things like networking, video, and filesystems for performant, and since not on the network side of things, not part of the code that needs to be in flux to respond to security threats.
On the other hand, Internet/Cloud is just one part of public facing networks....
(a private and so called secured wireless network is still public facing, unless the device is in a completely RF shielded from all directions underground bunker.)
https://www.nist.gov/itl/applied-cybersecurity/nist-cybersecurity-iot-programBut that is off topic for this thread.
I do not consider to insert the driver in the kernel.org repository. I know well how it "works".
And all we know that, as someone sayd: "The Linusx kernel was not designed to be friendly"
Since this discussion is in this forum, that is a given (not for kernel.org adoption).
I will reiterate what I said earlier. You
do understand the maintenance and other developments risks. Not everyone does, as many are naive about many things Linux.
Cool! And please don't take what I wrote to completely dissuade you. I'm just being realistic as to long term maintenance of out of tree Linux kernel modules.