Do we (eventually) want to apply this to all pointer types too, where we don't want the value of the pointer to be printed? Or is our current method for handling those sufficient?

Pointer types like *const u64 should already print "<pointer>" rather than an address/value if the "deterministic" option is enabled, for example like the implementation of deref_pointer_impl. The new wrapper is for types that are normally deterministic (such as u64), but aren't for some specific syscalls like ones that take a variable number of arguments or syscalls where integers are sometimes actually pointers. I'll add a comment to explain this better.

If you mean to reuse the new SyscallNonDeterministicArg wrapper in the deref_pointer_impl macro for example, I think we could do that, but I don't think we'd gain much from it.