For anything involved in the I/O stack this would be a complete non-starter because having a cache implies the existence of a filesystem which in turn implies the existence of all underlying modules. PCI, network stack, USB, etc can all be necessary prerequisites for that so it's a non-starter for anything involved with them too; at this point we've already ruled out most of the computer.

Also for embedded systems there often isn't a writable filesystem, and that is a huge part of linux's userbase.