Yeah, that's potentially compelling; if you've got UEFI enabled boards for those platforms. A quick search says maybe raspberry pi 4 supports uefi booting, which would be interesting.
I don't believe there are any POWER machines using UEFI. The standard POWER boot process uses OPAL (Open Power Abstraction Layer) instead. But POWER does use GPT disk partitioning, which is from the UEFI standard.
Someone has ported TianoCore to powerNV, but I've never looked into it. You could replace the hostboot payload with any binary, it's basically just an ELF file with a payload delivered, an initramfs in the case of skiboot/petitboot.
Not a lot of advantages in UEFI over petitboot, though.