Ok. but 28nm is nowhere close to where ARM is (7nm) and will be over the next few years (3nm). Smaller, faster, with multiple cores & on-board ML/Neural subsystems. The cost on the ARM side is always going to be lower due to the volume at which they are being dropped into phones. And if one wanted a faster x64 path, then why not AMD Rizen?
ARM isn't at 7nm, TSMC is. That's different from the PPC -> Intel transition at Apple 15 years ago: the tech is available to anybody who's willing to pay (while back then, Intel was 1-2 generations ahead of everybody else, and there was no indication that this would change).
The primary goal of a project like this is to prove the concept, and if 28nm NXP PPC chips are the sweet spot (enough performance for it to matter, unlike all those RISC-V micros; efficient enough to fit in a laptop without it working double-duty as a grill, unlike Power9 CPUs; cheap enough so that people are willing to risk it, unlike the otherwise fabulous TALOS workstation family) for that, that's not too bad.
In case this takes off, there can still be some entrepreneur who cooperates with IBM or NXP or whoever has an efficient Power implementation lying around and shrink it to the smallest process node they can afford, reusing this open hardware design, and send it off to TSMC. That option didn't really exist back in 2004.
