For C2x and C++2x it looks likely that they will drop support for sign-magnitude and ones' complement representations of signed integers, essentially mandating two's complement.

https://gustedt.wordpress.com/2018/11/12/c2x/

https://herbsutter.com/2018/11/13/trip-report-fall-iso-c-sta...

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p090...