A notable mention is https://ubports.com/en/ which is different from postmarketos in a sense that ubports uses old kernels with heavy patches. That means: good support for things, but difficult future.
PostmarketOS uses the newest kernels and tries to integrate their patches into mainline kernel, so that the reliability is maintained with all kernel developers.
It isn’t fundamentally incompatible, there is just a lack of drivers.
You don’t need new hardware, you need driver support.
I think they meant you’d have to design a combination of hardware that’s all compatible with Linux - that is, that has Linux driver support.
I’m not really so concerned with how it’s incompatible…