stdlib will never change, because it would break every PHP project out there. Many of the previous deprecations as been relatively easy to handle, like switch from each to foreach, or make sure that you don't pass null to stdlib functions, but changing the stdlib itself would instead be a complete nightmare.

Remember that many projects out there needs to support multiple PHP versions at the same time, it would be extremely confusing if the stdlib started to do subtle changes between versions and also hard to properly handle and detect.

Like if you would swap $needle and $haystack for strpos(), it would be nightmarish to statically detect in an existing code base which is the correct order and quite hard for a human.

Introducing aliases is also a bad idea, there already exists aliases in the stdlib and they only add confusion when reading code, that would be true for new aliases as well.

Named arguments alleviates the problem with argument order in exchange for more verbosity.

What PHP could do is to introduce primitive objects, e.g. $str->substr(...), however that would not guarantee a well designed standard library either, because RFC:s and emails is not a good forum for designing API:s.

I think the correct solution is to implement operator overloading and let the community design a standard library/libraries. Because of the massive performance improvements of PHP the standard library is no longer required to be pure C, it can either be implemented in PHP or wrap the existing stdlib.