How is a language supposed to make backwards incompatible changes, when it's eventually found that the original style contains substantial flaws? Would you wan

How is a language supposed to make backwards incompatible changes, when it's eventually found that the original style contains substantial flaws? Would you want the world to still be using K&R C? Because I remember the transition from that to ANSI C, and the special macros to make function prototypes work across both languages. The Python transition is little different.