Did you read it completely? (emphasis added)
Quote:
[...]will cause Bash to conform more closely to the POSIX standard[...]
"more closely" for me means it's already compatible, just not as strict.
As for the list of things that change, these are relevant for non-interactive use (aka "scripting"):
Quote:
12. Non-interactive shells exit if filename in . filename is not found.
13. Non-interactive shells exit if a syntax error in an arithmetic expansion results in an invalid expression.
16. Function names must be valid shell names. That is, they may not contain characters other than letters, digits, and underscores, and may not start with a digit. Declaring a function with an invalid name causes a fatal syntax error in non-interactive shells.
20. A non-interactive shell exits with an error status if a variable assignment error occurs when no command name follows the assignment statements. A variable assignment error occurs, for example, when trying to assign a value to a readonly variable.
21. A non-interactive shell exits with an error status if the iteration variable in a for statement or the selection variable in a select statement is a readonly variable.
28. The . and source builtins do not search the current directory for the filename argument if it is not found by searching PATH.
Ad 12: that shouldn't be a problem, as I think it's pretty common to check if something is there before trying to access it
Ad 13: pretty much the same. It's like checking the value of the divisor before trying to divide by zero.
Ad 16: I can't image a situation where I'd need a function that has a '%' or '/' in it...
Ad 20: If you can't keep track of which variables are read-only and which aren't...
Ad 21: see above.
Ad 28: So it works the same as command lookup, which requires you to use the (IMO) more readable ". ./filename" instead of ". filename"
And while I myself prefer the Korn shell to bash, it isn't without incompatibilities itself, as the POSIX standard shell was based on ksh88, while the current, ksh93, features quite some changes.