For the sake of completeness I want to add some more details on it:
Question is: How would separate logging work then?
- Some might have checked our ErrorHandler class available in TYPO3 Core, which was backported from TYPO3 Flow. This can be overridden by libraries or extensions or whatever by `TYPO3_CONF_VARS/SYS/errorHandler'.
A fairly easy task would be to extend the ErrorHandler class to be loaded which could even log into sys_log/beLog if people like that (I don't ) but the same way could be used to implement the PSR-3 logging there and deal with that in this place. What I mean is: The ErrorHandler class (using PHP's internal set_error_handler) allows to define exactly where to log a error/notice/warning/deprecation separately.
What I'm saying is: We're not limiting ourselves to use our custom GeneralUtility anymore, but centralize deprecation logging to the same way we deal with other parts of logging as well, having one "we do it differently for this kind of logging" less.