But they did not make old code correct. Filenames are still allowed to contain newlines. Shell scripts still need to be prepared to deal with that. Nothing really changed, they just added a feel-good half-measure.
It's a step in the right direction. You have to understand that for decades a vocal group of Unix die-hards has opposed any limitations whatsoever on the bytewise content of file names. The newline restriction in this latest version of POSIX may be modest, but it represents a dam breaking. When (obviously) the sky doesn't fall, the next version of POSIX will have a lot more filename cleanup.
