I don’t think this proof is particularly useful without considering the complexity of changes required to overcome this limitation. For example, pointers could

I don’t think this proof is particularly useful without considering the complexity of changes required to overcome this limitation. For example, pointers could theoretically use a variable length scheme (kinda like Utf-8), as long as the underlying hardware supported it or supported being able to pass only the next n bits of the pointer in something like a chained syscall. Of course that isn’t in the specification, but the transformation seems theoretically implementable without needing e.g. infinite length pointers for every access. In contrast, there is no way to coerce a DFA into becoming a Turing Machine (that is theoretically implementable on the DFA). So the proof is not necessarily wrong, but it might not be the right kind of proof to be useful.