Changes to the standard don't instantly, or even eventually, cause corresponding changes in implementations. Code that needs to be portable to many implementations will need to worry about line length limits for a long time into the future.

The Venn diagram of Fortran feature availability in the various actively maintained Fortran compilers is very messy, and the ISO standard is definitely not a subset of any of them. Standard-conforming code is not necessarily portable, and highly portable code is not necessarily standard-conforming, especially since Fortran '95.

The hard line limit length is at 1,000,000 characters not 10,000. Also, all major compilers currently have flags to significantly extend the line limit length.

You're correct about the compiler flags. 10K will be the line length limit; the 1M limit is for a statement length that can span any number of lines.