The C standard now says:
The ability to undefine and redefine the macros bool, true, and false is an obsolescent feature and may be removed in a future version.
That is, stdbool.h is deprecated. But no rationale is given and I couldn't find one. Do they intend on adding bool as a basic type for good or is there something else ?
If you happen to know why this is deprecated, thank you for telling me !
Why is stdbool.h deprecated?
It's not.
You quoted the following note:
The ability to undefine and redefine the macros bool, true, and false is an obsolescent feature and may be removed in a future version.
What this means is that the following paragraph may be removed in the future:
An application may undefine and then possibly redefine the macros bool, true, and false.
That does not mean that the header or its contents will be removed.