I like the idea of forbidding signed integer representations other than 2's complement, as it is de facto standard, pretty much nobody makes CPUs with non-standard integer representations, partly due to C programs assuming 2's complement integer representation.

What I don't like about this proposal is defining signed integer overflow as 2's complement wrapping. Yes, yes, I know undefined behaviour is evil, and programs wouldn't become much slower. However, if a program has signed overflow, it's likely a bug anyway. Defining signed overflow as 2's complement wrapping would mean not allowing other behaviours, in particular, trapping. On architectures with optional overflow traps (most architectures not called x86 or ARM), trapping would be much more preferable to quiet bugs. Meanwhile, while it is undefined behaviour, the implementation would be still free to define it, for instance in GCC it can be done with `-fwrapv`.