[TheLoafOfBread]

> For a long time everything else was stuck with custom built images for every device.

Like today with ARM boards, where each OS is custom-bent to each board.

[rbanffy]

I gather many of those are mainlined now. Bootloaders might still be needed, but I would imagine the bulk of the customisations for a couple "major" platforms is sorted out.

[TheLoafOfBread]

I would not call it sorted out, more like workaround. The problem will grow larger and larger until it will become unmanageable.