...having actually read those now, those threads didn't seem very helpful. :-/

Assuming the laws of physics actually does allow a halting oracle to be implemented, then at some point it would be easier to just implement it than to do these ridiculous cheats, right? As we rule out various possible cheats, that intuitively raises our credence that a halting oracle can be physically implemented, which contradicts the universal prior.

Hm, indeed. Actually, it occurred to me after writing this that one thing to look at might be the size of the device, since there are, as far as we know, limits on how small you can make your computational units. No idea how you'd put that into action, though.