Ihor Radchenko <yantar92@posteo.net> writes:

>> The only additional consideration is that compare function should be 
>> configurable. If a user access same files from Linux and macOS then it 
>> may be really annoying to get different order of entries in agenda. For 
>> most of Linux users it is better to use more smart 
>> `string-collate-lessp'. Some care is required to sort entries obtained 
>> from multiple buffers in predictable environment (locale, case 
>> conversion table).
>
> I agree. We can introduce a new customization -
> `org-string-sort-function' that will be used across Org mode to sort
> user text.

See the attached tentative patch.
I added a customization, made everything in Org obey it, and provided
some default options for MacOS users.