ACPI is, at the moment, the most labour-efficient way of getting suspend and resume working on the widest variety of hardware.

The alternative Mark is putting forward is for manufacturers to support Linux directly, which isn't going to happen until it's as dominant as windows. Compare the android situation, where you get manufacturer support but not updates or proper merges into upstream.

ACPI isn't going away on PCs, ditching it means ditching PCs as a target.

They said that for 16-bit CPUs and BIOS as well.

Why would anyone ever claim that 16 bit support would never go away? Not that it did go away: all the x86_64 chips still have 16 bit support.

And modern PC motherboards still ship with traditional BIOS support.

Never mind ACPI, the CPU chipset is already a delightful target for hackers:

https://news.ycombinator.com/item?id=7452912