Could it be possible we get this too in the workstation and laptop ecosystems?
(even for 32-bit Windows on Arm, back in the Windows RT times, this was the case. It's a shame that Microsoft decided to lock those down back then)
On more affordable Arm machines, Honeycomb LX2K has an official UEFI firmware (with ACPI) and NVIDIA's Jetson AGX Xavier has an official (but experimental) UEFI+ACPI option.
Those aren't complete yet in mainline when using ACPI. For the LX2K, onboard networking currently doesn't work when using mainline kernels. And for the AGX Xavier, you lose PCIe (until the quirk to support it there is merged, or the ECAM through PSCI patchset) and integrated GPU support.
When using a Windows on Arm laptop, most Qualcomm drivers only have device tree bindings, not ACPI at least at this point. As such, you might need to load a device tree at boot for a more complete experience. (you can look at repos on https://github.com/aarch64-laptops if you have one)
For SBCs, forget about almost anything not named "Raspberry Pi", for which... a third-party UEFI + ACPI firmware is available at https://rpi4-uefi.dev, which allowed the original RPi4 to be certified as SystemReady ES.
A lot of the things that actually drive making people implement UEFI + ACPI is that Windows, RHEL and VMWare ESXi require UEFI + ACPI to boot on 64-bit Arm.