Hi, thank you for your answers !
We were actually planning on switching to QtPy since our current abstraction layer Qt.py does not wrap PySide6 yet. However this will take some time to implement, and @UMD was very much looking forward to using C4D 2024 as soon as possible.
We are confronted to another problem that does not allow us to switch to C4D 2024 yet : the prebuilt PySide6 wheels available on PyPI are apparently not compatible with C4D's python DLL's.
The server/client model you suggest is something that would circumvent both of those issues, and it is in fact something that we have discussed many times internally, but changing our Pipeline's model at this point in time would take at least a year of planning and implementation.
@gheyret PySide is not bundled with C4D, you must install PySide yourself (using the wheels built by Dan Bradham for C4D since the prebuilt ones from PyPI are not compatible), and then you'll be able to import and use PySide in C4D 
They have yet to build one for PySide6 though, so using PySide in C4D 2024 will not be possible for now (there is an issue opened about this).
In any case, thank you for your time @ferdinand, we will figure out what to do internally.