There is no need to understand code when you review coding style, so I doubt there will be much improvement / refactoring.
But if the objective is :
then coding style is not very relevant.
Prestashop (even parts of it) is hard to interact with / integrate in other projects. Because it's monolithic, slow, hard to debug, not documented, and some parts are poorly designed.
Note: I have nothing against PSR-2, it will add some consistency in code, and it will be very usefull the day prestashop will include other components from the community (PSR-3 Loggers, PSR-4 autoloading).
I just see it as a "Nice to Have".