Proper macOS virtualization, for example.

Also, I do not want to have to upgrade my machine and OS every few years just to keep up with apps that stop working or installing, not because the hardware is no longer capable, but due to ridiculous obsolescence policies. Heck, I can not run the latest version of a lot of software (including basic developer tools) on one of my MacBooks, simply because it is running Monterey.

A proper package manager CLI is also sorely needed. Delegating that to Homebrew and MacPorts doesn't cut it.

Improve the speed of APFS. Like try forking off a job to create a bunch of git worktrees in on APFS vs EXT4 -- it's significantly slower. Deleting a ton of files, cloning repos, hardlink performance, etc; APFS performance is poor compared to just about any other Linux filesystem.

Make installing Linux on it easy